https://www.economist.com/britain/20...for-a-drubbing
The scale of the defeat matters to more than just politics nerds (although, we admit, we are rapt). If Mrs May loses by a narrow margin—fewer than 50 votes overall, say—she might just about be able plausibly to claim that, with a few tweaks, she could get the deal through on a second attempt. The EU is unlikely to agree to any big changes. But a few warm words in the formal political declaration that accompanies the legal text of the agreement might be enough to give wavering Tory rebels a ladder to climb down, should Britain approach its planned departure day on March 29th with no deal in sight.
If, on the other hand, Mrs May loses heavily—by more than 100 votes, for the sake of argument—it is hard to see how further fiddling in Brussels could change enough minds in Parliament to get the deal through. At that point the government would have to consider stronger medicine: a general election, a second referendum or leaving with no deal at all. If she loses the vote, Mrs May must outline her plans to Parliament within three working days, by January 21st. It is looking ever more likely that Britain’s scheduled exit will be delayed. And the odds are also shortening on Britain not leaving at all.