I agree, this encounter deserves a dialog option. Seems random you end up fighting them after you both worked to ill the spectator.
You can also kill the drow while they are petrified. I found it interesting they have an AC while petrified, and it's not automatic to hit them. Seems funny whacking away at a statue with a war hammer and missing. Once you reduce them to 0 HP they turn back to normal and you can loot them. Easy way to get a few out of the way before waking the spectator.