Prima guide says Servos can't die of old age (obviously), fire, starvation (obviously), or sickness, but all other deaths are possible. Incidentally, I've never seen a report of water killing a Servo. Making it run amok, yes, but not killing it.
You can't normally kill a Servo from anything that requires motive depletion. This means standard fire, standard electrocution, ghost/vampcoffin scares, are all out. Only sudden-death will work.