I've generally had long absences taken care of by nasty surprises crawling out of one of the umpteen plot threads I've got going. Since I'm not nice at all to my characters, it ain't hard to find something awful that'll take them off stage for a while. Betrayal, death, sensitive smuggling operations, even the simple need to clear the mind of daily concerns and research/design/implement revenge (and conduct a thorough review of where things went wrong in the past, and how not to repeat the same mistakes) -- I've used all of these activities to explain that off stage time.
I do write during this downtime. I do try to keep up with IC events via forums, blog reviews, e-mails and IM sessions. The invention of EvEGate now makes that even easier.