So...I had some help from Five Star on this one. I actually waited 24 hours to do anything besides dry it. I was worried that adding water would spread the stuff farther, but they suggested adding lots and lots of water, as you all did.
I added some water, soaked it up with paper towels, and let it dry. The carpet is...well, completely fine as far as I can tell.
As far as my roommate goes...we don't know. The starsan bottle was somehow knocked over and the cap was somehow on the opposite side of the closet.
So many mysteries...
Oh well, at least there's beer.