I once made the players be kobolds left to guard the warren, and adventurers attacked. I gave them "time points" they could spend on movement or trap placement or digging, etc.
And then I ran the adventurers, while the kobolds tried to stop them from looting the treasury or killing the children. Four lowly kobolds vs. high-level adventurers. It was cool, though they failed.
It could also be a free download or any other online source. We're just looking for something we can start and finish all in 8-10 hours. A good way to wrap up our 3 years of roleplaying together.
That's a great old-school module with a cool plot and a short interplaner hop to a demi-plane based on a magical France (no jokes please). Strong plot with some neat fights.
Problems:
1) It's oD&D so it's conversions a-go-go for you!
2) No way you can finish that up in 8-10 hours. No way.
My advice? B2 Keep on the Borderlands
You don't want to leave anything unresolved. So why not just take a trip down memory lane instead?
Why, Tomb of Horrors, of course... that way, the ones moving won't have to lug those PC notes with them, and the rest of you can start a new game with new PCs...