Whatever else happens with Brexit, no one in British politics will ever again underestimate the power of a timetable. The pressure of the article 50 clock ticking down forced Theresa May into the compromises that make her deal unpalatable to MPs. She has tried to pass the pain on to MPs, hoping that the grim consequences of missing the deadline would force them to settle for her plan. Earlier this week, in an act of parliamentary jujitsu, the former attorney general Dominic Grieve turned the timetable weapon back on May, securing an amendment that sets a limit of three days for the prime minister to say what comes next if her deal collapses.

Running down the clock should eliminate options and force decisions. So far that hasn’t worked. Instead, the same volume of Brexit bluster has been compressed into an ever tighter space, which, in accordance with the laws of political thermodynamics, raises the temperature and increases the danger of something blowing up.

Brexit law has now been amended and re-amended so many ways that power lies neither with the government nor with MPs

May has been holding the lid, keeping the pressure on. It is her deal that MPs will almost certainly reject, and hers alone. Brexit itself does not depend on this particular prime minister. It is easy to forget that, when the whole business has felt like a Shakespearean tragedy with May at its centre: the hostage to pitiless circumstance undone by her own flaws, consumed by a megalomaniacal sense of duty – a monstrous hybrid of piety and arrogance.

But next week begins the great disentanglement, when threads of what parliament might endorse will be separated and sorted, regardless of what May wants. Brexit law has now been amended and re-amended so many ways that power lies neither with the government nor with MPs. Parliament gets to say what it thinks should happen – the prime minister isn’t bound by law to do it, but would surely not survive long in office if she flatly refused.

And so the race is on to form some cross-party coalition that can agree on some kind of plan: any plan that is not May’s one, and doesn’t involve flying off the no-deal cliff edge. As one cabinet minister put it to me recently: once that coalition is found, “it is then effectively the government”. It is premature to say that discussions are under way to form some national unity administration, but the idea is being seriously kicked around among pro-European Tories who imagine that disaffected moderate Labour MPs, worn down by dissidence in Jeremy Corbyn’s regime, can be recruited to a temporary arrangement that gets the country safely through the next few months.

In my experience, remain-leaning Conservatives underestimate the gravitational force of Labour tribalism, regardless of who is leader, but it is certainly true that dismay over Brexit has created some surprising friendships that cross partisan lines.

The two main propositions competing to prove their viability are the second referendum (under the banner of a people’s vote), and a Brexit model that keeps the UK inside the single market and the customs union, once characterised as Norway plus and now rebranded “common market 2.0”.

Neither camp can yet muster a majority. The “Norwegians” say their numbers are artificially low because many Tories who support them, including cabinet ministers, have to pretend to back May’s deal right up until the moment it fails. But Tory people’s vote supporters also claim to have sleeper cells of ministerial endorsement. Labour MPs on both sides argue that their leader will eventually come to see the logic of their preferred option.

It is a peculiar rivalry between factions who agree with each other about most of what is wrong with Brexit. They would almost certainly back each other’s proposal if their own were eliminated. The people’s vote side would prefer common market 2.0 to May’s deal. Many of the common market 2.0 brigade would go for a referendum if they were more confident that public opinion had shifted so far that the result would be a slam dunk for remain. Meanwhile, each side has to manage the awkward geometry of coalition-building across the floor of the Commons. When a Tory declares for a people’s vote, it makes it harder for the left to sign up. When former remainers back common market 2.0, it is harder to sell it to leavers as a bona fide Brexit. It is the classic Rubik’s Cube conundrum – lining up the colours on one face ruins another one.

UK faces prospect of no Brexit if May's deal rejected, says Hunt Read more

The one thing all can agree on – the only proposition for which a Commons majority has already been demonstrated this year – is that Britain should not crash out of the EU without a deal. The problem is that no deal is the scenario that requires the least action. It is what happens if everyone just carries on being pretty much as they have done, failing to organise around any one goal. MPs can rail against the idea of no deal, but that doesn’t prove it can’t happen.

Many things were unthinkable before they started to look feasible, then suddenly became inevitable. Brexit was one. A second referendum might be another. May somehow bulldozing her deal through parliament cannot be ruled out completely.

She has said many times that the UK leaves the EU on 29 March – but many officials believe that an extension to the article 50 period is inevitable. Even if parliament approves a deal, there isn’t much time to pass the subsequent enabling legislation. We are at the stage of the Brexit drama where every possible outcome has been ruled out at some point. The final act has to involve some shift in perceptions of what is possible. Birnam Wood is on its way to Dunsinane. The Brexit tragedy that was all about Theresa May’s ambition and misjudgments is coming to an end.

The sequel is a story of rebel bands in parliament competing for power as it flies from the prime minister’s hands.

• Rafael Behr is a Guardian columnist