The government with it's absolute majority would have to lose the vote. It would have to vote against itself.
Exactly.
And don't forget that turkeys don't vote for Christmas. Any MP who isn't absolutely certainly they'd win won't go near the notion of potentially voting themselves out of a job.
Now any general election held right now would end up de facto as a second referendum on brexit - it would really be the only issue. So any MP whose views on brexit don't align with their constituents is going to be feeling very nervous about a vote. And that includes a mighty lot of Tories. We've already seen Zac Goldsmith licked out, effectively for being anti brexit - that will focus a lot of minds.
So lets take a few example - in my own constituency we have a pro-brexit MP, yet we voted over 70% for remain. The LibDems have always been very high profile. Our MP could easily lose against an overtly pro-remain LibDem so she isn't going to want to go near a general election any time soon. And there are plenty of similar tories, particularly in the home counties in a similar position.
And the reverse is true - lets not forget that the majority of tory MPs are pro-remain - and plenty of them will be representing constituencies that voted leave. They'd be deeply vulnerable to UKIP who'd campaign that they are the only party really to represent the brexiters.
And don't forget too that MPs are people, with mortgages to pay - are they really going to risk losing their jobs in a few weeks rather than be assured of at least 3 and a half years further, and critically they'd think that by 2020 the brexit issue will be settled and people will move on from whether their MP's views on brexit aligned with their own or not.