The first time I tried to do it, it just didn’t spawn for me at all, and I actually was able to abandon the quest and try it again.
The second time is when AFTER turning in the quest, the mob spawned and despawned.
I totally agree – what if someone were to D/C and died from the mob? They can never get the rune now?
You also can’t see other mage’s spawns, so you can’t even group up with someone to try and get it