We (almost) did that. team went to the left, I took the right alone. Lured wizard out, team-killed him, I went in and killed the Shrieker, traverse to the left, meet up with team, go in.
Problem: a gazillion of knights that followed us up the stairs as soon as we entered the structure, leaving us almost no time to aim because we were forced tojump constantly due to the Knight's OHK melee attacks.
I'm the only 31 in the team, so I can take about 1,15 melee hits - at one point I decided to turn in g'horn for pocket infinity and just ran/jumped in circles around the Deathsinger. got her down to somewhere between 10-20 percent a couple of times, but never managed to kill her. It got really late, so we quit.
One question: what triggers the countdown? entering the area? killing the shriekers?