one of the problems with a mage or warlock combi in an instance without a tank or healer will be:

- a boss is immune to any slow effects
- a boss is immune to any frost effects which reduce the movement speed
- a boss is immune to any fear effects.
- a boss is immune to any stun effects

most of the bosses are standing between the next passage of an instance.
so you can only clear the trash before the first boss, then turn around and restart the instance.

btw. it's annoying when one of your DDler dies - you can't resurrect him because you don't have a healer class in your party