My plan, and this is just something on the fly because there is almost NO way (unless I am missing something) to get in the priestess' tower other than the door, is to draw one of the bird things down and slide past the drow to cause them to have to either pay attention to me or the thing and slip into the tower.
Ezraen's thought is that if he can grab the spellcasting foci and escape without dying, we can jump off the waterfall.