He asks you for a favor. But I've compleated the temple and he does not collect it.
Should I stay or should I go?

Go ahead and leave. The "favor" will be called in much later on, in a different chapter.

<center>Nightowl2</center>

i never quite understood what that favor was all about. why would he want you to
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kill those glaberazus or whatever? why was he summoning them?

Game said he was stopping the demons from ever corrupting people like the "Sisters" again, permanently. I guess those demons where somehow connected with the one in the altar. Doesn't make much sense though.

When you kill a demon, he is baned from the material plane for 1000 years or so, so he probably lured them there to kill them, but things turned out badly and he used his favor to get your help.

According to Salvatore, its only 100 years.

It depend on the kind of demons, but I have don't remember any numbers, 100 is possible.