An auto attack should kill it.
Any time I've ever seen anyone die on this fight, it's not from not killing their mirage, it's dying to AE damage while running back (usually unlikely for me), or more than likely, an add (haze dudes I think?) is chasing them beating on them. I always try to kill the haze as they spawn to prevent this.
If anyone does die for me, I usually just revive and run back.
Alternatively, if your priests get the adds that are realllllllllllly far away, they kill their add, then the named spawns back on the group, and it takes 20 years for the priests to run back to the group because they are so far away. On my tank I usually just pop a group damage reduction/stone skin and wait for them.