At level 68 mages get a skill called invisibility;
If you cast it you will "fade" for 5 seconds. After those five seconds you will become invisible. But if anything hits you in the five seconds you're faded the effect will be canceled.
So, when your party is about to get wiped, just pop invisibility and start running away. After 5 sec you'll become invisible, the mobs will stop attacking you, and you wont die. While you're invisible run to a safe spot, and you're saved. This will save you some repair costs and a corpserun. Try to use frost nova and blink first, because if anything hits you in the 5 sec before you turn invisible, the effect will be cancelled.
I thought this was common knowledge, but haven't seen anybody use this except for me...