I think I would have had a last combat with the whole group and let them go down fighting. Sometimes those can be fun fights. They give it their all, use all their items and tricks, and take down as many foes with them as they can. I mentioned earlier that we once ended a campaign with a party combat... which was unwittingly driven by the GM himself being a bit of a jerk.
What happened is we were fighting Kobolds in a foggy setting. I finished off my foe and said "I turn around" (looking for another enemy) and the GM says "You see a figure behind you." and waits for my action. I won't get into the details, but based on how the fight had been going and the GM's lack of elaboration I assumed this was another Kobold. So I said I swing.
The GM looks at another party member and says "What's your AC?" at which point we both respond with "Uh, we're human height. The Kobolds are short, we'd be able to tell the difference." The GM pretty much said "You said you swing, so you swing." So I swing and miss. So the guy I swing at says "Ok then, I swing back."
Now, at that point we just thought it was funny and were going to leave it at that... but the GM decides to have a NPC 'vital to the plot' attack the guy I swung at, who then swung back at me. It's at this point that we basically decide we've had enough (obviously there were previous issues with the GMs style). An all out party combat breaks out, I think there were seven of us... three were left standing at the end (one of which had sat out the fight). The 'vital' NPC was dead.
At the end the GM thinks I'm going to rez the dead NPC (I'm a Ranger/Cleric), but instead I walk over to her body and take the Mace of Disruption she has, which was placed in the game for my character, but when the GM made us roll off for loot, when it appeared, the NPC took it cause she rolled higher.
I have to say, it was one of the most fun fights I ever had in D&D. The GM had this totally dumbfounded look on his face the whole time. It was pretty funny. Because, once the NPC went down, there was nothing for him to do. We were fighting each other. Campaign over!