I was just thinking about the Stefan-compulsion / Tyler-siring thing, and a thought crossed my mind--that it really raises the stakes on actually killing Klaus. One of my big problems with last season's unkillable-Original-Klaus plotline was 'why bother killing him? With the power of 100 dead witches, surely Bonnie could a)trap him in the tomb, b)sink him down the Mariana Trench, or c)launch him into low-earth-orbit. Because of Stefan and Tyler, that doesn't work anymore.