Saturday night I was into the first set at the local Ramada Inn, when a violent thunderstorm came through. Lightening hit the building and knocked off all power for more than 24 hours.
I always keep a surge protector between my equipment and the a.c., and keep it where I can reach it immediately. Never needed it before, but when I heard the crash, I hit the switch on the surge proctector. The lights in the room flickered a time or two and went out. It was several hours later before I was able to find that I was very fortunate. No loss of information and no damage.
A friend who also does a single, on the nights I'm not there, using a Roland sequencer and a PSR740 had left his equipment on the bandstand also. He lost all memory in the sequencer. The equipment itself seems to be o.k. Fortunately he had backed up his data recently, but it still was necessary to do a restore operation.
Moral: Use a good surge protector and unplug your gear when you're not going to be there. And be certain all info is backed up, with at least one copy of the backup in a different location. I'm sure we all know this, but I know I get lazy sometimes and forget.
Don