It's the end of an era for two of Disney's tent-pole franchises.

This year marks the conclusion to Marvel Studios' three-phase "Avengers" epic – with a movie appropriately titled "Endgame" – and the final, yet-to-be-titled film in Lucasfilm's most recent "Star Wars" trilogy. Analysts are already predicting big box-office returns for both movies. Some suggest the pair of films together could generate upwards of $1.3 billion to $1.5 billion in total ticket sales in the U.S. alone.

Yet while both studios are slated to release films that wrap up their respective sagas, only one seems to have a clear future: Marvel.

Marvel Studios has a detailed slate of films prepared for 2020 and beyond, including sequels to "Doctor Strange" and "Black Panther" and a solo Black Widow film. Lucasfilm, on the other hand, has been quiet about its big-screen plans going forward, aside from a few announcements about possible trilogy projects that have been light on details.

Also complicating things for the "Star Wars" movie franchise is a decision to slow down the release of Lucasfilm titles. That move came in the wake of the lackluster box-office performance of standalone film "Solo: A Star Wars Story."

"These are the two biggest box-office moneymakers in Hollywood right now, and not only are we about to witness two historic finales, but the storytelling decisions each brand makes from here on out will define the next era in moviegoing," Erik Davis, managing editor of Fandango, told CNBC.

Disney had a banner box-office year in 2018, and 2019 looks to top that. The House of Mouse pulled in $2.9 billion at the domestic box office, or about 25.5 percent of the U.S. film industry's total ticket sales, according to data compiled by Comscore.

This year, analysts predict that Disney's 10-film slate, which includes "Captain Marvel," "Avengers: Endgame," "Star Wars: Episode IX," "Toy Story 4," "Frozen 2" and three live-action remakes of beloved animated classics, could bring in $3.5 billion to $4 billion in the U.S.

However, the company likely won't be able to top that growth the following year, and the uncertain status of the record-breaking "Star Wars" film franchise is a big reason to be skeptical.

"You can only stay at your peak for so long, and 2018 and 2019 for Disney really has been what they have been building up to for the last close to 15 years," said Shawn Robbins, senior analyst at BoxOffice.