Sure but I don't think it will get to that and most MPs pretend to do the MP job. I expect if Mr Johnson ceases to be PM he will resign* his seat before any election.
My guess is that he'd stay until the election, due to the wrath he'd incur if he caused another potentially humiliating by-election, and the personal humiliation he'd suffer if the seat was lost, because it would still be a vote on his performance. But, yeah, obviously just spitballing.
Sure but I don't think it will get to that and most MPs pretend to do the MP job. I expect if Mr Johnson ceases to be PM he will resign* his seat before any election.