All eyes are on the British parliament for Tuesday's crucial vote on the key Brexit texts negotiated with Brussels.
With the parliamentary arithmetic seemingly stacked against British Prime Minister Theresa May, the question on most minds is not whether the deal will be approved but rather by what margin it will fail.
EU officials say the Brexit deal is not up for renegotiation, but few doubt that they will do everything they can to prevent Britain from crashing out of the European Union without measures in place for an orderly departure.
Here are some of the possible scenarios.
A) PLAIN SAILING
On Tuesday, parliament approves the withdrawal agreement and the political declaration on future negotiations, which have already been endorsed by EU member states. The European Parliament also ratifies the texts and they are in place to ensure a smooth transition when Britain leaves the EU on March 29, 2019.
From the outset, this outcome looked unlikely. Since parliament began debating the Brexit package, the odds have fallen further.
B) ROUGH WATERS
Parliament narrowly rejects the deal on December 11. May returns to Brussels to seek amendments in order to put the agreement to a second vote.
As analysts note, this approach would most likely work if her defeat in parliament is not too large. "If her deal is defeated by a big margin - say by 30 to 40 votes - she may no longer be in control of events," warned Mujtaba Rahman of Eurasia Group, a think tank.
Furthermore, the EU side has made clear that the fundamentals of the withdrawal deal are not up for renegotiation, so any changes would likely be cosmetic.
In order to bolster support in a second vote, May could also seek a softer Brexit - for example by keeping Britain in the EU's customs union - in a bid to win over opposition lawmakers who would like to stay more closely aligned with the bloc. This would likely be an easier sell in Brussels.
C) MUTINY
If parliament overwhelmingly rejects May's Brexit package, this could put her leadership into question, potentially bringing Britain closer to a general election. It would also strengthen the resolve of those calling for a second referendum on Brexit.
In this case, any minor changes to the deal are unlikely to be enough to placate its opponents.
To avoid an unregulated Brexit in March, Britain may seek an extension of the two-year Brexit countdown triggered by Article 50.
This would give Britain more time to resolve domestic political issues, for example by holding a general election or a new referendum, and find a way forward that is acceptable to Britain and the EU.
Several opponents to the Brexit deal argue that other options are available. These range from a "managed no-deal" scenario with a series of mini-deals to regulate key areas such as medical supplies and aviation, to temporary membership of the European Economic Area (EEA) alongside other non-EU members such as Norway.
An influential group of eurosceptic Conservatives in Britain has proposed an extended version of the EU-Canada free trade deal.
This would remove almost all tariffs on industry, agriculture and fisheries trade, while also covering financial and other services. Unlike the EEA model, there would be no membership fee.
However, it would take time to negotiate such a bespoke deal. Some eurosceptics suggest postponing Britain's departure from the EU, while others say it could be done after a no-deal Brexit.
D) THE WORST-CASE SCENARIO
If the British parliament does not accept the withdrawal deal and it cannot be ratified before March 29, this would put Britain on track for an unregulated Brexit.
EU rules would cease to apply in Britain as of March 30 and the country would drop out of shared arrangements - such as common air traffic rules or trade deals with third countries.
Businesses and people would likely suffer from administrative chaos and backlogs at Britain's borders, potentially including that between Northern Ireland and the Republic of Ireland. Efforts to keep that border open have been at the heart of Brexit negotiations.
This would also lead to uncertainty for British citizens living in the EU and vice versa. On the upside for London, it would be released from many remaining financial obligations to Brussels.
British eurosceptics say such predictions are part of a "project fear" to persuade people to accept the deal.
They say the two sides would be able to agree a series of rapid, sectoral mini-deals to minimise disruption before they negotiate an alternative, Canada-style deal after Brexit.
E) NO BREXIT
On Monday, the European Union's top court could decide that Britain has the right to change its mind about Brexit. This would embolden those calling for a second referendum.
May has already warned parliament that the choices it faces are "this deal, no deal, or no Brexit".
However, remaining in the EU would also be a tricky endeavour at this stage and would likely leave Britain bitter and divided.
