traiditions are an odd thing. It's also very friendship specific. Even if I did want to get a good friend a gift for "going away" I wouldn't get them a group gift. I'd do something on my own. Friendship, interestingly enough, usually ends up being a relationship shared between two people... not one person and a group.
All in all I'd rather pretend people aren't even leaving rather than give them something for abandoning me. =0