Either Jeremy Corbyn or Owen Smith will be elected party leader on 24 September. What could happen after the vote?

Labour’s turbulent summer, which kicked off with a riot of resignations in the aftermath of the Brexit vote, will come to a formal close in Liverpool this Saturday, when the result of Owen Smith’s challenge to Jeremy Corbyn’s leadership is announced. But even if Smith is soundly beaten, few expect peace to break out, after a bruising contest that has exposed the fault lines between the warring sides in the Labour movement. Here, we ask what might happen next.

1. Smith wins: a new battle commences

Few Labour insiders are expecting Owen Smith to win. But there is little reliable polling, and Saving Labour, the lobbying group set up to campaign for a replacement to Jeremy Corbyn, claims to have done an effective job signing up trade union affiliates and non-members willing to pay the £25 to register to vote.

The Pontypridd MP has presented himself as a unity candidate and promised to offer Corbyn the new job of Labour president – in charge of the grassroots party. But Corbyn has made clear he would not accept such a post.

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A Smith-led Labour party at Westminster could lure back many of the big-hitters who either refused to serve Corbyn originally or deserted him after he sacked Hilary Benn as his shadow foreign secretary in the aftermath of the Brexit vote.

But a considerable cohort of pro-Corbyn MPs would be likely to return to the backbenches and make trouble for the new leader, and he would have to decide whether to pick a battle with Momentum, the pro-Corbyn grassroots campaign group.

Early on in the campaign, Smith appeared to suggest he would seek to win over Momentum and its many thousands of activists, but his attitude has hardened over the past few months. The tough language of his final speech – describing Momentum as a “party within a party” and comparing it to Militant, the hard-left group expelled from Labour in the 1980s – suggested he might be prepared to try to drive them out.

2. Corbyn wins: happy ever after

Facebook Twitter Pinterest Jeremy Corbyn and ally John McDonnell. Photograph: Leon Neal/Getty Images

Corbyn told reporters last week that he was growing an olive tree on the balcony of his Westminster office and would hold out a branch to rebellious MPs and urge them to return to his shadow cabinet.

Dark talk of deselections for disloyalty won’t have helped, but some refuseniks are considering accepting his offer, particularly if the party’s governing national executive committee passes new rules introducing elections to some shadow cabinet posts, at a key meeting on Tuesday – a plan that would then have to be ratified by party conference.

Even Labour MPs critical of Corbyn believe the party has a responsibility to provide an effective opposition to Theresa May’s government, and should abide by the members’ choice. “We were told to put up or shut up; we put up, and we lost. Now we have to provide the most effective opposition we can”, said one.

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They also acknowledge that Corbyn’s performance at Westminster set-pieces has improved recently, and admire some of the young Corbynistas who have stepped up to shadow cabinet roles vacated during the coup - the shadow education secretary, Angela Rayner, for example, who some believe may be being groomed as a potential future leader.

If Corbyn and his allies, including John McDonnell, stick to the conciliatory script, there could yet be just enough unity to create a more complete shadow cabinet; allow Labour to present a united front at Westminster; and help to heal the rift between the party in parliament and many of its new members.

3. Corbyn wins: war of attrition

Facebook Twitter Pinterest Chuka Ummuna is to stand for election to chair the home affairs select committee. Photograph: Jack Taylor/Getty Images

Despite all the talk of splits in Labour, including from Smith, it is hard to find MPs preparing to flounce off to another party, or none. But there are plenty who believe there is little to be gained from returning to serve under him.

Some are seeking roles on high-profile backbench committees – Hilary Benn and Emma Reynolds hope to chair the Brexit select committee, for example; Chuka Umunna and Yvette Cooper, home affairs.

Others plan to work together to provide an alternative voice of opposition to the government from the backbenches, or throw their energies into thinking about centre-left post-Brexit policies, a part of the political spectrum they believe Corbyn’s Labour has abandoned.

Under this scenario, while Corbyn struggles to fill all the posts in his shadow ministerial team, he will be scrutinised closely by a series of well-known Labour figures with powerbases of their own, and little interest in making his life easier. One Corbyn ally predicts it will be a war of attrition.

This summer’s leadership campaign has been bruising, and many at Westminster regard it as strengthening, not weakening Corbyn’s hand. Yet it may not be the last challenge he faces before the 2020 general election.

4. Corbyn wins: the party splits

Facebook Twitter Pinterest Tim Farron has issued an open invitation to moderate Labour MPs to join the LibDems. Photograph: Getty Images

In Westminster, many Labour MPs who feel unable to serve on the frontbench are growing increasingly frustrated, but rumours of splits have been repeatedly scotched.

Labour rebels were rumoured to be mulling a deal to allow more MPs to stand on a Co-operative party ticket, which has held an electoral agreement with Labour since 1927 that allows them to stand joint candidates.

MPs were said to be ruminating signing up more than 100 new MPs for the Co-operative party to allow them to appoint their own whips and develop their own policies. The Co-operative party’s leadership has said it will oppose such a move, however, saying the party was “not a vehicle to be used by one political faction or another to advance their own agenda”.

At the opening of the Liberal Democrat conference on Saturday, Tim Farron issued an open invitation for moderate Labour MPs, especially staunch remainers, to join his party. “My simple offer to those liberals in other parties is: do you know what, maybe it’s time to join a liberal party,” he said.

Party figures are poised to approach centrist Labour MPs at risk of deselection in their constituencies after boundary changes, with an offer to allow them to stand as Lib Dems. How receptive Labour MPs will be to such a suggestion, with the Lib Dems at 8% in the polls, is uncertain.

5. Corbyn wins: a new party within a party forms

Facebook Twitter Pinterest Badges, posters and T-shirts on sale at a pro-Corbyn rally by Momentum in July. Photograph: Jack Taylor/Getty Images

Few moderate Labour MPs, especially those in safe seats, have any appetite for a physical split.

For many, it is a point of principle not to admit that control of the party is lost for ever. If Momentum is, as it is seen by many, a party within a party, Labour moderates believe they too must create a similar movement within the party. It is understood that such a movement would be launched shortly after a leadership election loss to Corbyn.

The tactics would mirror Momentum’s rise from Corbyn’s leadership campaign in 2015 – this time using Smith’s campaign resources, including his database of volunteers, as a backbone for a new movement.

Labour sources told the Guardian the new movement would need to be open and transparent to avoid the negative publicity MPs received during the perceived “corridor coup” to get rid of Corbyn over the summer.

The movement would launch with an umbrella identity for progressive Labour groups in parliament and outside, with researchers hired to develop policy. Moderates in the party who back such an endeavour see it as a way to try to take back the party without having to operate cloak and dagger and avoiding the trauma of a physical split.