How did I know somebody would make a rage thread about this. You know you can lead Companions around traps I've done it about a billion times. Also, usually when my companions get hurt by a trap they don't die they keep getting up and getting hit by the trap again its pretty entertaining to watch they AI just keep running into the same trap over and over again.
I've had a companion disappear before due to the sliding blades [hallway, axe blades slicing you up] trap before. Not sure if they died, but they were jammed off the playable map [launched like a giant punted them into the void is my theory].
It's annoying, but, I just stopped taking companions on them.
To be fair though, I suspect the OP is referring to Quest Companions/Dungeon Companions, not the traditional companions. You're really not able to tell Quest followers and the like what to do, in my experience.