Both Garfield and Dilbert had the same trajectory: They started with a much broader premise, which included more characters and a stranger kind of comedy, which narrowed and flattened out over time, until the premise had been reduced to a few characters and a tiny world and the humor had been simplified and made more universal to the point it had lost all of the unexpectedness which is the essence of the best comedy.
Better strips, such as The Far Side and Calvin and Hobbes, had a much flatter trajectory, keeping the same ambit and comedic sensibility throughout their runs, which makes it impossible to imagine them being handed off to anyone else. Garfield, which is essentially a legacy strip at this point given how little Davis has to do with it, could keep going for decades, like Hi and Lois or Blondie, with no real change now that it’s reached its final, simplified form.
But of course it won’t. Because newspapers won’t, at least in their historic form, the form conducive to multi-generational legacy strips; the piling the legacy strip barnacles are clinging to is slowly rotting, and the broader ocean of the comic world isn’t as friendly to creations which simply sit and filter royalties.