I don't think history will be kind to Johnson, even aside his total lack of personal qualities.
I do wonder how much of it is self-delusion or whether he knows but can't admit his failings in office out loud.
His three main achievements in his own mind seem to be Brexit, Covid and Ukraine.
With the Brexit vote 6 years ago, we still haven't completed the process of leaving to anyone's satisfaction. The new leader will have to unpick this mess, particularly with regards to Northern Ireland and also implementing the border regime required to inspect imports. Most of those issues come down to Johnson not being willing to admit what was being
With Covid, the consensus at the start was 20K deaths would be a reasonable result. Unless someone slipped an extra zero in his memo I don't think you can count it to be a success.
Ukraine, I doubt any other leader would've done anything differently, other than perhaps react more quickly to the refugee relocation process.
He can get stuffed and earn a few million on the speaking and writing circuits and then when he is ready to come back and try again, hopefully the mess he leaves behind will be more evident and the public will quite rightly reject the immoral charlatan.