Only the new stuff
You can still buy countless numbers of calendars, books, coffee mugs, etc. with his stuff. He did 7 cartoons a week for years, so there are thousands of cartoons to choose from. He can never pick up a pen again and still make a comfortable living reselling his old stuff over and again. He IS a genius!
I'd love to see him return to active cartooning but doubt it'll ever happen. Like "Bloom County" and "Calvin & Hobbs", "The Far Side" has gone on to the other side. I miss them all. There are some good cartoons out there but none make me laugh as much as those three did.