It's an interesting what-if because the way Diane was in the last few seasons was the result of Long's telling the producers well in advance she was going to quit, so the writers scrambled to make her less organic to the show and less likeable. Notice how much less she interacts with people apart from Sam compared to the first couple of seasons, and how irrational she gets. Cheers managed to thrive after she left (even though I prefer the Diane years, the overall quality is just higher), and Long, sadly, got the short end of the stick.