Yes they can die, they usually dont though because they drop all agro as soon as they're at about 5% health. If you've lost your follower though, and by lost i mean misplaced, after a couple of days in game time a message will appear saying your follower got bored and went home.
So far though the only follower thats died on me though is the war dog Vigilance, he died as he lived, by jumping infront of my arrows.
So far though the only follower thats died on me though is the war dog Vigilance, he died as he lived, by jumping infront of my arrows.