Our pal Greg Ehrbar has written a long, fine history of Will that covers a lot of things I didn't mention about him. You can read it over on the Cartoon Research website.
As far as I know, no plans have been made for any sort of memorial gathering. I've spoken to a lot of Will's friends (and Will had a lot of friends) and they all seem to want one. That's an indicator of how much we don't want to let him out of our lives.