I'm playing as Bandit, Mendoza has opened the big gate into the mountain and the monastery is overrun with lizard men warriors.

I've done all the other quests (killed all the lizardmen intruders, the Steadfast Lizard warrior, and so on) that are a part of this mega-quest, except for giving the library packages to Sirius so that he can impress his Master, Abrax. The walkthrough I looked at indicates where Sirius should be, then adds "(for some reason if you're playing as a bandit, you won't see him here)" but doesn't mention where he might actually be.

Another walkthrough says he is Abrax's lab, behind the red magic barrier, but he's not there either. And a third walkthrough says that if I'm playing as bandit then Sirius won't be in the lab.

Anyone able to give me an idea where in the monastery I might find Sirius?

Since no walkthrough I've come across mentions where Sirius will be for Bandits, then is this quest impossible to complete? Too bad really since there is more than 1000 exp points at stake.

EDIT:
Ok, so I found Sirius and he's not even at the monastery. He is at Severin's farm, and he isn't interested in talking to me at all. So, as I suspected, the quest to secure the volcano keep is impossible for a bandit player.

EDIT of the EDIT:
The quest to secure volcano keep can be completed after all, without having anything to do with Sirius. You just have make sure to kill ALL the lizard men in the monastery. Apparently I missed one even after covering every room and area looking for Sirius. I had gone over to Jasmin hut following lizard hunting party to get map of the temple, and when I returned to monastery, suddenly the lizard warrior came at me from out of nowhere, and then when I spoke to Ignatius about something else I could finally complete that quest.