Rarely happens to me but if someone gets aggro and is simply not getting close to me so i can grab it off him, i dont even bother following him, if we wipe, fine not my problem.

But to many Dps and healers are automaticly running around like headless chickens the moment something is chasing them.

Simply not bothering with thsoe people, let them have fun with the mob that is after them, if they refuse to get closer then i refuse to help . Simple