Yes Avalyon is right, Nalzaxx came back but only to heal the plague. Whether you believe he caused it in the first place, and whether you believe he is now a god or not is an ingame matter and was always meant to be so.
Nalzaxx did linger at the Temple for awhile in order to give the people there some chances to roleplay with him. However he has not come back to restart the Temple, or act as an all powerful NPC for them.
You can now consider Nalzaxx gone for a very long time. Of course he may make appearances in the future as a quest character, but he is never coming back to resume the role as the leader of the Temple and to cause havoc in Gobiath again.
There are a number of reasons I used Nalzaxx to heal the plague. Firstly, as many of you have appreciated, the irony that after causing so much misery to the island Nalzaxx comes back to save it cannot be missed. Secondly he is well known as being the Lord of Pestilence and Plague and has a lot of history with the older characters. It gives it that extra impact for the older players rather than if it was some random new NPC. Thirdly, he's my baby and I never considered his story finished. I wanted to clear up a few questions on where Nalzaxx went and where he goes now. Rather than merely dissappearing.
His reasons for healing you won't be clear to those who just see Nalzaxx as OMFG Evil L1CH man Kill!!1! However to those that actually know the character it will make sense.
I know you and I have had our differences in the past Patric, and I think thats where a lot of your animosity to this quest comes from, but I can assure you you needn't stop playing because of this quest. I can assure you, nothing will change. Dain wasn't broken out by a mummy called frank. He was infact broken out by playercharacters that assaulted Siltaris and stole her key.
How did he become a god? You are born as a god and cannot become one. Consequently he is a liar.
The younger Gods were not born as Gods. Read up your history young padawan. They were mortals from Nabranoo who were chosen by the Elder Gods.