Survivability is not the problem i believe, well from what i have seen anyway. (coming from someone who has rarely played SP so dont be offended)
I believe the biggest problem is dispellers, and the easiest way to stop this problem is to add a dispell function to the spell "Vampiric touch". E.g If the spell is dispelled the dispeller recieves a "X amount" second silence.
I know this is the same as UA from the afflicition tree for locks, but seriously it would go a long way for SP.
This may have been brought up im not too sure so dont flame please! I'm just suggesting ideas
so what do you think?