first boss in spellplague caverns disappears.

questionor

First boss in spellplague caverns disappears. My guess is he fell through the world. During the fight for no apparent reason he just poofed. His health bar was still at top and the damage already done did not reset. We killed all the spawnerss and he still did not come back. We killed the other adds that spawn independent of the spawners numerous times with breaks between waves to do nothing and he still didn't come back. Deliberately wiping group did make him reappear.