What's the point of celebrating now that he's dead?
My great grandmother used to tell all of us -- if you're planning to come to my funeral: don't. Use the money and time you'd spend then and come visit me now.
I think now is a reasonable time to mourn. A great mathematician is no longer around to give talks (I went to one a few years ago and thought it was very neat), and if you know him personally then you won't get to see him and converse with him anymore. That's very sad. Sure, he may have done abstractly great things, but there's no denying there are sad aspects to it.
But as for celebrations and parties, those should be done while the guy is still around to enjoy, I think.