I managed to kill Trollbane as a lvl 40 Frost Mage.  I didn't have the quest when I did it - I just happened to end up in the area and wanted to see what he dropped (I got squat).  Some useful info - I cleared out the guards outside on both sides in case I needed to kite him around there.  Also, the 2 guards around him can be pulled without aggro'ing him.  I hit the one to the right of Trollbane and he and the one to the left of Trollbane both charged.  I took care of those two and then pulled Trollbane - a few frost bolts, frost novas, etc and he was dead.  It was pretty easy, to be honest, and more importantly solo-able and do-able at lvls much lower than Trollbane.  Just make sure you kill him before all the respawns around him and the Sanctum.