Dungeon World, Going Lightly
So, a variable cast from week to week, and a conceit that means they have to return to civilization, or at least safety, at the end of every session. So you're probably not going to, for instance, break your session in between phases of a boss fight, or halfway through a tense infiltration, with the confidence you can pick things up cleanly next time. But that's probably fine, if you're after something in the mold of, say, Wizardry where you've got a town and you've got a giant crazy dungeon and I don't know what else you need.
If you like the idea of the party as an adventuring company, I would recommend having the party as its own adventuring company exploring the dungeon out of their own volition or taking work for hire, rather than necessarily being part of some larger enterprise. That way there isn't this presumed pressure from outside that people might chafe against and people can take obligations or not as it suits them. Bonds will already work to bring people together - you don't need an "and also your paycheck" rider.
If you're engaged in regular old dubiously-safe dungeon-crawling, rather than halfway through an action scene, you can have an end-of-session move about pulling out of the dungeon early. I've had some success with this one:
When you beat a hasty retreat from the dungeon, everyone picks a favorite item they found and a favorite stat. Then:
If you have someone with +2 Int to map your way out, take +1.
If you have someone with +2 Wis to keep an eye out for hazards, take +1.
If you have someone with +2 Str to lead the way through the heavy obstacles, take +1.
If you have someone with +2 Dex to quickly manipulate the light obstacles, take +1.
If this isn't your first time in this part of the dungeon, take +1.
If you've got a guide, or someone else's well-drawn map, take +1.
If there's someone you have to guide, or something complicated to carry because of size or fragility, take -1.
For each of you carrying more than half your load (round in your favor), take -1. You may voluntarily abandon loot to take yourself under this limit.
Now roll (just once for the whole party) to see what happens on your way back to safety.
On a 7-9, each of you chooses: abandon your favorite treasure or mark a debility in your favorite stat. On a 6-, both.
On a 10+, each of your chooses: lose all your other treasure or mark a debility in a different stat of the GM's choice. On a 12+, also choose: the GM will tell you something interesting about your favorite treasure, or take +1 ongoing in your favorite stat until the next time you Make Camp.
And when you're swapping people in, you can engage in the fine old Apocalypse World tradition of love letters, which are custom moves designed to show the passage of time for a character. Such as:
So you spent some time out hunting! Great! Tell me what you were stalking and where it lives, then roll +WIS. This counts as tracking, if Rockjaw can help with that. On a 10+, all three. On a 7-9, pick two. On a 6-, pick one, but it can't be the last one:
You take out your quarry and bring back a trophy. I'll roll treasure depending on how dangerous it got and run the conversion by you.
You take note of (or perhaps notes of) interesting features of the trail and your quarry. Bank 3-preparation about this creature and climate. You can spend it when it makes sense.
You don't take it on the chin, starting off hit for the monster's damage and a debility of your choice.
Love and kisses, your GM