i like the first idea rather than the second - or maybe he'll appear in the city every now and then, hopef he's just at the start of the game, making you be mayor, then he leaves ad pops up every so often
you'll probably get promoted as you arrive. or you'l have some back story like "you were from [old town name] and have received a promotion to be mayor in [new town name]" something like that
As much as it would be nice for Tortimer to retire, I'm pretty sure he's not going to be there. Nintendo pretty much has already killed him off. In City Folk, he didn't do anything, ever. Other than events. The rest of the time he was sleeping.
But if you want to be positive and keep to hoping he will be in the game as a character, it's just as likely that he retired and called you in to replace him and might give you tips or something.
I don't care about Tortimer. Like I don't see what the big deal about him is. Maybe it's just me...
We should find that out at the round table