One variant on the "it was all a dream" (which is one of the lamer ways to hit the reset switch) is to say it was all a nightmare (as the spell). Now the PCs get to try and find who is nightmaring them. Of course just saying "You all know absolutely nothing like this would have happened in my campaign, we're going back to the last point I DMed" is probably what they were expecting anyway. If I loan my car to friend for the evening, and he comes back sometime the next morning with 500-some miles on the car and front end damage, you can bet I'm going to insist that he pay for all the repairs and maybe something for the wear and tear (the closest I can come in real life to hitting the reset switch). You could also give the players some token amount of XP for their trouble (excluding the sub DM if you are quite justifiably feeling vindictive).