Unfortunately that doesn't quite follow, Hopkirk -- or, at least, it's something that would have to be put to an electoral test.
In the first place, while it may be political suicide, what if it were judged from the top that Brexit is after all "national suicide"? In that case -- or, indeed, in any other case -- wouldn't it be refreshing to have a politician turn around and say "my career is not worth keeping if it means implementing this policy"? That's not to say that such a judgement about Brexit is correct but the point is that maybe Theresa May might think it would putting the country before herself, so political suicide isn't necessarily a guarantee that Brexit would happen.
But in any case, the arithmetic of General Elections may well mean that it would be politically triumphant to oppose the referendum result. After all, 16 million people did vote to remain in the EU. If those 16 million could be persuaded to vote for a single party then almost certainly that party would then win a landslide. Perhaps, even, Theresa May could pitch the Conservative Party as standing up for the Remainers over the Brexiters.
In practice I don't expect this to happen. But it could. Even that fact ought to be enough to demonstrate that there is a basic, and potentially quite horrific, flaw in our electoral system.