What would you all do?; roll a new character and class, or just transfer realms for the new guild?
It's really up to you, but for me, I rerolled. The highest level horde character I have on a different server is a Lvl 35ish Undead mage, but with addons like "questhelper" and the bumps to XP Blizzard has added, levelling isn't the chore it used to be (it's still a chore, but not as bad). And since this is probably never going to be a raiding/endgame guild, helping each other level is what I see this guild as being for (that and the social aspect).
And if the long grind to 80 is too much like a second job, you can always roll a death knight. No one else is doing that.