Most of the time there is not much you can do to get away. Barring special tactics like the water in the deadmines you are going to hold aggro until you die (although certain mobs in instances actually have leashes as we found out when facing Eranikus in Sunken Temple).
The first way to help prevent completely wiping is to have a warlock on hand to put a soulstone on you. This won't stop a wipe but will greatly increase the speed at which you can restart on your run. Just make sure as the stoned person you don't die close to the mobs' reset point so that they won't aggro you when you activate the stone. Also remember to not activate the stone until all mobs have reset and it is clear. You don't want to waste that soulstone.
If you don't have a warlock on hand your best bet is to stand and fight. If the battle is down to one or two mobs and your party is down to two people you can still pull it off. As a priest you have a few tricks up your sleeve. If you have the mana go into a quick heal spree, fire up your shield, and open fire. With Shadow Word:Pain and Mind Blast/Smite you can do some damage and it might just do the trick. Never forget Psychic Scream if there isn't another group of mobs around that you could aggro. If you are seriously outnumbered then the wipe is inevitable... just get ready to make a corpse run and reevaluate your strategy so it hopefully doesn't happen again.
- mjdoom
Edit: added another thought
The first way to help prevent completely wiping is to have a warlock on hand to put a soulstone on you. This won't stop a wipe but will greatly increase the speed at which you can restart on your run. Just make sure as the stoned person you don't die close to the mobs' reset point so that they won't aggro you when you activate the stone. Also remember to not activate the stone until all mobs have reset and it is clear. You don't want to waste that soulstone.
If you don't have a warlock on hand your best bet is to stand and fight. If the battle is down to one or two mobs and your party is down to two people you can still pull it off. As a priest you have a few tricks up your sleeve. If you have the mana go into a quick heal spree, fire up your shield, and open fire. With Shadow Word:Pain and Mind Blast/Smite you can do some damage and it might just do the trick. Never forget Psychic Scream if there isn't another group of mobs around that you could aggro. If you are seriously outnumbered then the wipe is inevitable... just get ready to make a corpse run and reevaluate your strategy so it hopefully doesn't happen again.
- mjdoom
Edit: added another thought
Stormrage:
Flyndar (60) - Dwarf Priest - Tailoring (300), Enchanting (300)
Minimagi (60) - Gnome Mage - Herbalism (300), Engineering (301)
Galreth (60) - Human Warrior - Blacksmithing (300), Alchemy (300); Critical Mass by name, Lurker in spirit
ArynWindborn (19) - Human Paladin - Mining/Engineering (121)
Flyndar (60) - Dwarf Priest - Tailoring (300), Enchanting (300)
Minimagi (60) - Gnome Mage - Herbalism (300), Engineering (301)
Galreth (60) - Human Warrior - Blacksmithing (300), Alchemy (300); Critical Mass by name, Lurker in spirit
ArynWindborn (19) - Human Paladin - Mining/Engineering (121)