People coming back will have to relearn their class because many have changed, the shaman most of all. I spoke to an old friend who played a shaman back in the day. On raids she said she slowed, dotted and healed the cleric. I pointed out that in modern raiding she wouldn't even be grouped with a cleric, she'd be with melee DPS and their sole healer and DPS enhancer and that she shouldn't have a single DoT loaded even with 13 spell gems. That got an 'ugh' response.