That I'm too lazy to run away. :o Nah, I basically stay in the background when battling a boss that's tough on mages.
I love drain life. It heals and at the same times take hp from your opponent. But you have to be careful with the timing. It has a little delay (one of the best things about it imo), so if you use it on an opponent with low health, chances are you will kill him before you're able to steal hp from him. On the other hand, if you already know you'll be taking damage, you can already cast it, take damage and heal almost instantly (and at the same time deal damage yourself). I use it a lot more than mana shield. Between the 3 seconds for heal respawn and drain life, you can recover an awful lot of hp. :) (Something you won't be able to do when all damage gets deducted from mana instead of hp.)