In regards to this thread...

Summoned creatures killing the "boss" still prevent a quest from being closed properly. I had my character solo the Rat Barricade quest, and intentionally let a summoned creature kill the boss, then tried to close the quest, and it did not give me the option to complete it. :(

Hm! Intriguing.

Just to make sure, can you test this on one other quest that's not Rat Barricade?

I've had my animal companion kill the troglodyte chieftain, it worked fine there.

Rather unrelated, I've seen the Urdlenite priestess die to acid (?) from their own trap, leaving the quest unfinished.

I am wondering if perhaps the Rat Barricade quest has issues of its own.

Traps which were not set by a person on the quest killing the questgiver are still an issue.

I am wondering if perhaps the Rat Barricade quest has issues of its own.

That may be. Tested out Boggs quest, and the narrow tunnels (eyeballs) quest. No problems resulted from killing the bosses with summons on those quests.