What Happens if PCs Get Stuck in the Dungeon?

If you run an RPG only when all your players are available, and some of your players have lives outside your game and will have to sometimes miss a session, then eventually your campaign will die due to non-attendance.  (You play week 1, but then you skip week 2 because Alice has work, and you skip week 3 because Bob is sick, and you skip week 4 because it's Clarence's kid's birthday, and by the time week 5 rolls around everyone has forgotten about the game.)

So the obvious solution is to run your game even when only some of the players are available.  And the corollary is to end each session somewhere safe, where you can easily swap out PCs between sessions if necessary.  Then 80% attendance is no problem at all.

Unfortunately, in the eighth session of the Arden Vul campaign, the PCs got teleported somewhere that they didn't have an obvious safe way home from, and then kept looking for treasure right up to the time limit, which included lifting the lid off a sarcophagus with 3 minutes to go in the session.  Opening a sarcophagus at the very end of a session brings very real risks of a fight starting that they can't finish until the next session, and that's what happened.

So how do we deal with PCs ending the session in the dungeon?

First, this is where the correspondence between real time and game time breaks.  The players will return a week later, but for the PCs, no time has passed.  As far as the PCs are concerned, it's still Demmasday the Third of Legarios.  It's still their eighth delve into the Halls of Arden Vul.

Second, as long as the PCs are paused in the dungeon, no XP is awarded, and no previously awarded XP can be spent.  They have whatever loot they found, but they can't easily sell it yet.  They don't get a week of free healing, or a chance to roll Carousing or Research, or time to go shopping, or even an hour to cast healing spells and rest.

Third, there's no easy way to swap PCs in the dungeon.  The ones who are in the dungeon are the ones who will be in the dungeon until they get back to town.  So if a player can't make it next week, they'll have to pick else someone to run their PC.  (At least for the start of the session; if they make it to town partway through the session, they're free to swap PCs.)

Overall, I expect that after this happened once, the players will be a bit more aware that it can happen again, and might somewhat modify their tactics to avoid that outcome.  Then again, they really like loot and XP, and might press their luck again to avoid coming home empty-handed.  It's ultimately up to the players when to go back to town; it's up to the GM to design appropriate rewards for doing so and consequences for failing to do so.