They were raised in America but came of age in a broken immigration system. For many, long since returned to Mexico, change will come too late to build the lives they once planned

For millions of undocumented migrants who have spent years in the US legal shadows, the rupture of the political deadlock on immigration was the realisation of what once seemed a forlorn hope.

But even if the moves to fix America's broken immigration system result in a deal that once seemed so elusive, for many others it will come too late. Those are the people for whom the pressure of living without proper legal status bore down too hard, and they returned home.

Most of them will never be allowed back: anyone who has lived illegally in the US for more than a year and re-entered illegally is permanently barred from being admitted to the country, unless they can argue for an exemption on the grounds of "extreme or unusual hardship". And there are no plans to change that particularly harsh provision in America's notoriously tough immigration regime.

Many former undocumented migrants return to Guadalajara in Mexico. It's been dubbed "Mexico's Silicon Valley" and those who return from the US with bilingual skills can easily find a high-paying job at call centers in multinational corporations. Here, there is a ready-made support system for people trying to find their footing in the country they were raised, but barely know.

These people, like most of their friends and coworkers, still hope to return one day to the US, believing the results of immigration reform to be unpredictable; and many of their family members still live in the US without papers. For this reason, the Guardian has agreed to use pseudonyms.

Natalia, 23, moved to Charlotte, North Carolina, when she was eight years old, and stayed there until she graduated from high school. Her parents were told they could get documents through her older brother, who is a US citizen, if they returned to Mexico. Since Natalia wasn't going to be able to get a degree or a job in the US, she returned with them to Mexico five years ago, age 18.

The first time she applied for a visa she was denied, and learned that returning was going to be more difficult than she imagined. Today, she is still desperate to go back: "If I go back, I'm gonna start from the day I graduated high school – applying to college, looking for jobs."

Natalia did not learn of her undocumented status until her senior year of high school. Until then, she had expected to have a normal life after graduation. "I saw myself going to college, getting a degree, getting married, doing whatever I studied, working, being independent and maybe eventually having kids. I saw myself doing things and being successful – I sure as hell didn't see myself here."

But despite the knockbacks from the legal process, Natalia is hesitant to return to the US through the plentiful illegal avenues. "It's risking your life to go hide," she said.

"Yes, there are chances of maybe trying to go back illegally, but I wouldn't want that, because I'm just going to go back to hiding or getting a minimum wage job," she said. "It would be a kind of crappy life, so if I'm going to live a crappy life, I might as well do it here, where I know I'm pretty much legal and I can try to go to school, and get a license and get a job."

While Natalia misses the US lifestyle, her family, who she helps support financially, is still in Mexico and she values the security of legal status.

"I mean, as much as I love the US and I love and miss my friends and my life, the only thing that keeps me here and kind of gives me a positive attitude towards it is that I don't have to hide from anything or anybody," she said.

The U.S.-Mexico border in California. Obama's win was promising for the Latino community – especially in California. Photograph: Sandy Huffaker/Getty Images

For some, the decision to leave the US meant saying an indefinite goodbye to their remaining undocumented family members who cannot visit Mexico because they would not be allowed back across the border.

Carla, 23, moved to Mexico from Sacramento, California when she was 19. Her mother, who is separated from her father, still lives in the US with Carla's younger sister, who was born in the US. "I said goodbye to my mom knowing I wouldn't see her for years and years," Carla said.

Carla spent a total of 12 years in the US, and she moved back to Mexico after trying to cultivate a life without papers for two years after high school graduation. She worked at restaurants where managers overlooked her status, attended community college and spent time with her friends and family, but was constantly frustrated as her friends attended better schools and had more fulfilling jobs.

"The main reason I left was that I realized that I wasn't going to get to do those things, and I would be watching everybody do the things I wanted to do," she said.

Now, Carla constantly thinks about going back to the US, but because of the length of time she spent living there illegally she, like Natalia, is subject to the permanent bar.

Carla says she can barely carry a full conversation in Spanish, but admits that if life in Mexico was more like the US, she would not mind staying.

"As much as I really don't like living here, some days more than others, I feel okay knowing that if I want to get a driver's license, I can go get a driver's license," she said. "It would be a pain in the ass, because it sucks here, because it's nothing like it is over there [in the US], but I could do it."

On that flight back to Mexico, Carla remembers thinking "I'm screwed". But the day after she stepped off the plane, she got a job and now makes more than most of her Mexican family members, even those with a college education.

"Sometimes I think maybe I don't want to go back, I'm already here, what are the chances that I will get papers and be able to go back? I mean I hope, but I'm old enough to be at least a little bit more realistic that it won't be something that I can do."

Unlike Carla, Sofia, 21, did not know she had been living in the US without papers until she started applying to college when she was 18. That was when her parents told her she did not have a social security number.

"I had all these ideas of how my life was going to be after high school, and when I found out that I didn't have a social or that I couldn't work or that I didn't have the same opportunities that my friends have, that was devastating," she said.

Sofia calls herself "illegally legal". She, her parents and her siblings possess temporary visitors' visas. People who have these visas are prohibited from going to school and working in the US. Sofia and her family have violated that prohibition for more than two decades.

Her final year of high school coincided with Barack Obama's 2008 election win, so she decided to stick around her home in Venice Beach, California, for a year to see if things would change. Obama's win was promising for the Latino community and especially in southern California it seemed like the Dream Act – long-delayed immigration reform that has languished in Congress for years – would pass in the near future.

But in the end, Sofia thought waiting around for change was too frustrating, and she told her parents she wanted to get a fake social security number. They didn't want her to do anything that would diminish her chances of getting documents if reform happened. That's when she decided to leave.

"A lot of really good things happened, but I know that at the end, there are always people that are going to say no, and I wasn't going to stay and wait," she said.

Carla had visited family in Mexico a couple times, but said US media reports made her afraid of living there. "I couldn't imagine myself in Mexico – I'm gonna get robbed, I'm gonna get mugged."

She now calls that position ignorant and said that career and education opportunities are better in Mexico. "I don't want to go back because of opportunity anymore, my opportunity I have here. I want to go back to it because of la modo vida – the way of life, the quality of life."

Mexico is still plagued by corruption, and Guadalajara has seen a significant increase in cartel violence in the past few years. Carla argues that if the borders were more open – allowing passage for the 11 million undocumented migrants who won't leave the US because they are afraid of not being able to ever return – the resulting migration free-flow would also benefit Mexico. "So many people would be able to come back, study law and finally change the government to be like the US."

Carla thinks that broader immigration law would have a positive effect on the Mexican government for the same reasons she and her friends are able to have high-paying jobs and get good educations in Mexico: her US upbringing. "We live here, but we have the mentality of somebody who lives in the US, and we look for more," she said. "People here assimilate, they don't aspire to be more."

• On 5 February 2013, the third paragraph was amended to make clear that migrants who have lived illegally in the US for more than a year and re-entered illegally are permanently barred.