i belive he specifically took the rights to the art with him in anger over whatever happened to the project. however im not sure as to the patent status of the game concept. assuming you could find a new artist you should be legally safe even without permission. if you really are i encourage you to do so, i would be thrilled to see it continued
If you'd like some help, I'd be willing to lend a hand. You'll need all-new art assets, animations, everything. In fact, it would be best to create a spiritual successor rather than a remake. Who knows what legal action their disgruntled team-member who ruined it all in the first place may desire.