The way I do that with a 1:1 time system is to have the adventure resolve off-screen, and we pick up years later in game time as well as real time.
If I was strict about resolving such things "off-screen" they wouldn't get to do much adventuring in play!
They leave town during session 1, reach the adventure site, and wade in; we leave off with them three rooms in.
A 1:! week passes, duirng which time in-character they'd have either finished that adventure or died trying (there's no way in hell I'm going to violate both setting consistency and player agency by arbitrarily saying they go back to town or just sit tight for a week for no reason). So they're back in town again. Lather rinse repeat. End result: the players get lots of practice at travelling to adventures, but that's aobut it.
If something is unresolved for years I'd generally regard it as a 'dead adventure' and move on.
If I knew that group was never going to resume then yes, I'd mini-dungeon* the adventure to its conclusion; mostly to free up those characters for later use in other adventures by players still involved, but partly because that party's success or failure in that particular adventure has, in theory, some long-term story implications there and elsewhere.
* - mostly for use when updating long-retired characters who have done some adventuring in the meantime, a while back I developed some charts and tables that could boil an adventure down to just a few dice rolls - how "big" it is (i.e. is it a one-and-done hit job, a massive megadungeon, or something in between), how rough and tough it is, how lucrative it is, how mission-successful you are, and how long it took in game time - with corollary rolls jumping off from there if needed e.g. if an adventure comes up as "tough" then the PCs involved need to save or have Something Bad happen e.g. death, level loss, major curse, that sort of thing.
I've got long-term data showing what the odds are of each of the various Bad Things happening in an adventure - ditto for Good Things e.g. suddenly gaining a level or stat point, a major blessing, finding/gaining a wish, etc. - which I used to make up these tables. Before that, I did these mini-dungeon things by the seat of my pants, which worked but wasn't as successful or varied in outcome.