I'd be quite content if he slipped on a wet tile, banged his head and died. As long as he goes, the job is done and the world would be a better place.This is going to sound bad but, if ever you prayed for someone to just die horribly and in pain, it would be for Putin.
One of the most likely options would be for one of his body guards to slot him with two rounds in the back of the head.