It is true a fortnight is a long time in politics, and people can change their minds. It is also true that on the current arithmetic Mrs May is not just facing the loss of a crucial vote, but she is facing a landslide defeat. So far she has only mustered around 220 Conservative MPs who will probably vote for her proposal, with maybe 10 others from Opposition parties who might defy their party whips to support her. This leaves around 400 MPs of all parties who have said they will vote against. A defeat by around 170 would be a huge blow. The announcement by Sir Michael Fallon on Monday that he was against the Agreement was another big loss for her, as most had him down as a reliable government supporter.
What could she do instead? She could announce she has taken soundings and realises that her attempt to find a set of compromises with the EU has not produced an Agreement that suits either side or any party in the Commons. She will therefore cancel the debate and vote. Instead she would have to go back to the EU and tell them the draft Agreement they like is unacceptable to the UK Parliament. It either needs to be materially amended or the two sides need to agree on the UK leaving in March 2019 followed by free trade talks swiftly afterwards, or preferably starting immediately.
The amendment route looks unlikely to succeed. The EU has a long history of offering the UK too little too late to retain the country in its legal and political system, and will not take kindly to being told they have overdone it again. The rewrite necessary to the 585 page Withdrawal Agreement would be so wide ranging to make sure it can pass the Commons that it seems unlikely it could be achieved, even given lots of goodwill from the EU side.
This leaves us with exit and free trade arrangements, which is what will remain assuming Parliament does vote down Mrs May’s motion. Opposition forces in Parliament may want to find a way to delay Brexit or to push the idea of a second referendum, but this would not honour the results of the referendum. It would also require both the consent of each member state of the EU and new legislation in the UK in a Parliament with no government majority for any approach that entails deviating from implementing Brexit. It is no longer possible even if Parliament wanted it to legislate for a referendum and hold one prior to exit day on 29 March 2019.