Cult of the Eyeless: Possible programming glitch (solved!)

.....OK, we went down into the rift, waded through Ghoul Town, whacked all the various Beholders and other vermin we encountered. and got to the final room. Grabbed the second piece of the rift device, and the Eyeless One appeared on schedule. As it happens, prior to this I had Hexxat place a number of traps on the path leading to the final room. Mr Eyeless was actually killed by her traps; we didnt use the rift device at all. Mission accomplished, right? Wrong!
.....Here's the problem. There was still a charge left on the rift device, since it hadn't been used to kill the big boss. When I went back to the Temple to speak to the Avatar to report our success, he was nowhere to be found. Was this because the game assumed that the objective hadn't been accomplished since the device was unused? I seriously hope that I don't have to repeat the entire quest from the very start. Ick.
.....Here's the problem. There was still a charge left on the rift device, since it hadn't been used to kill the big boss. When I went back to the Temple to speak to the Avatar to report our success, he was nowhere to be found. Was this because the game assumed that the objective hadn't been accomplished since the device was unused? I seriously hope that I don't have to repeat the entire quest from the very start. Ick.
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Fun fact: unlike other unkillable creatures in BG2 that use min-HP immortality items, the avatar merely has huge HP and 100% resistances - the method used by BG1 creatures that you're not supposed to kill. Lower the magic resistance, and he dies instantly to a Cloudkill. (Reward for doing so: absolutely nothing)
OK, this is just dumb. I did speak to that dieased guy, but only because I was expecting him to say how grateful he was at being freed. So, if I had not ... totally by accident ... spoken to him, the Avatar would not have manifested, despite our having killed the Eyeless One, and the quest would never have been finished? That's ridiculous!