If it comes back up for a while, we should certainly post the global announcement and also send out an email to all members. Although we wouldn't be able to tell them exactly where we're going—maybe ask people to check b77 or TORC for that news?
While it might annoy some people to hear from a site they're no longer interested in, it would be better than having anyone who does like to stop by periodically, or who might have been taking a break, think we're gone for good.