All depends what Watterson does with his estate when that time comes. Watterson has shown to have a greater resolve for his position on this than most others and it wouldn't surprise me that he has this figured out to prevent anything until the copyright runs its course.
J.R.R. Tolkien himself sold the film rights to United Artists.
Also, for what it's worth, it's hard to imagine a better executor than Christopher Tolkien. He basically spent his entire life serving his father's artistic interests.
I don't think it's sad at all, I think it's a touching act of love. To spend your life caring for the work someone else left behind is generous and something I find admirable.
Hate to say it, but give 50 years, I wouldn't be surprised if Calvin and Hobbes turns into what you described.