VDW is not your shit as fire mage, prefer playing arcane here. But in general dps here does not matter a lot, focus yourself on killing Rot Worms, Supressers and Blazing Skeletons. Use your burst for them.
Amplify Magic VDW.
Focus Magic a healer (Hpaly or RShamy). Refresh it after each time they come back in your world.
If you want to have some fun during this boring boss, try to catch you mates with Snow Fall when they was hit by the archmage's Column of Frost.
As Arcane: If you have Incanter Absorption you can get a very nice SP buff on this boss. By absorbing frost bolts.
Nothing special to notice in heroic mode.