According to rumor from informed sources, Dick himself also kept some 35mm film and other secret things.
I do not feel that it is necessary for people to have saved the artwork in order to restore this film. It would be helpful if ever someone tries to finish the unfinished animation, but as long as you have the various cuts of the film on either film or video in decent quality, all is okay. And we do have that, so all is okay.
Any artwork that's been saved is simply icing on the cake.
And yeah, this is great news. More news as it develops.
You can get your Thief cafepress stuff at cafepress.com/cobbler, a little site I made for Eddie Bowers' page. If you have any special requests, let me know.