By last opened area I mean whatever the last portal was that was opened. In the living quarters of the hunters, you should have met the demon on your way in for a conversation. In the elemental portals you walk in on a conversation between an NPC there and either the nature spirit or demon.
All the earlier portals must have worked fine; it is only the last one you need to worry about if Zixzax doesn't resume opening portals once the attack is over.
If you do end up having to kill Zixzax, he will not remain hostile (his opinion of you may drop a little).
