I also think that Johnson will walk on his own terms - but I don't think it'll be until after the next election (assuming the Tories remain in the lead in the polls until then): If he goes before the next election, he'll be remembered in 10 years' time as a flash-in-the-pan who was briefly PM during some fairly turbulent times. On the other hand, I'm sure he knows he's a good campaigner, and with the current state of the parties, the Tories are looking very likely to win in 2 years or so with another thumping majority. If that happens and he's still leader, he becomes the first Tory leader since Margaret Thatcher to outright win 2 general elections in a row. If you had Johnson's ego, which way would you want to be remembered?
Good points there
I wonder if he's planning a post-Covid election - say May 2022, only half way through a notional five year "term" but soon enough to get some kind of "bounce" from having got over Covid ("Get Covid Done" - even if the stats won't quite fit his narrative) and before the worst of the post-Brexit problems become apparent (the post-Brexit problems have been disguised by the disruption caused by Covid and by the Suez Canal difficulties - retailers are happy to blame a generic "disruption to global shipping" than give people unpleasant truths about the problems they're encountering after leaving the single market/customs union)...
...that way he gets to walk away with his head held high in late 2022/early 2023, before his successor gets bogged down in things like surrendering some of our "sovereignty" to keep trade moving, or the constitutional problems caused by a further Scottish referendum - leave the difficult stuff for your successor!
That would also mean that the 2022 "local" elections wouldn't be a mid-term protest vote (where lifelong Tories felt safe backing whatever Farage is calling his next party) but an "us versus them" proper General Election (it might be tough to recover from a damning mid-term protest vote, where traditional Tory voters stayed at home or decided that they were okay to vote for a nUKIP) - just a hunch - he won't want the humiliation of being voted out at an election and he won't want to get bogged down in messy negotiations or details - but he can't be seen to leave without Getting Covid Done so can't leave just yet
The unknown is what'd happen if the Tories were ever behind in the polls (for more than a blip)? They've been leading opinion polls most weeks since the global financial crash which was almost fifteen years ago, so we don't know how the party will react if they are seen to be behind. Especially a lot of current Tory MPs are from the 2017/2019 elections (as the "old guard" of MPs like Ken Clarke were shuffled out and Tories won unexpected seats in places like South Yorkshire), so they've only known the good times, they've only known power, they've only been ahead in the polls. There was a great William Hague quote I heard on Matt Forde's Political Party podcast, where he said the "the Tory Party are right behind their leaders, right up until the point when they aren't" << i.e. the change when it comes will be pretty swift - especially as the large number of new MPs never spent time in opposition and might get jittery at the prospect of a defeat.
In normal times, you'd expect an England victory at the Euros (or World Cup) to guarantee the PM a boost - but we've already seen the Home Secretary to defend people's right to boo the national team and backbenchers say that they are boycotting matches because Something Something Woke Something, so they might not be able to claim the reflected glory... (they probably will try to claim it, let's face it!)