Mavie left because she took up her podcast(s), which cut into HM time. You can still see her on Skype fairly regularly; I don't auto-invite her anymore because she's usually doing something else I don't want to interrupt, though I'll drop off a "hi, how ya doing?" note occasionally.
Mirth & Constance I don't remember.
GoldenScimitar, DeadShallRule & Deadhorse just kind of didn't care anymore. I think Deadhorse was a good friend of DemonToSome, and stopped showing up after Demon got banned for the 2nd or 3rd time.
MistressOfHorror ended up doing something new that took up a bunch of her time. BabyFirefly got tired of us making fun of her Paris Hilton obsession. HQ and Panda are back doing school and working (HQ is impossible to get a hold of). Crispy is working out life issues. Got a message from PuppyMonster that she might stop by HFest '13 at some point. Vengey hangs out more on FB now. DG is just really busy.
Don't know what happened to TwistedSista & Mikki, they kept hanging out on Skype for a while, but then vanished from there, too.
Don't know what happened to SheSaid, MorgueX, DethBanger, MachetteMassacre, or PyroPyrahna at all.