Taylor Dent and John Isner? Is Dent done due to all the injuries? And was Isner just a flash in the pan?

Dent is back playing, with his back troubles now behind him. Isner was diagnosed with mono just before the French Open and is out indefinitely. I guess he didn't talk to Federer about how you can actually play more tournaments, because stopping playing with mono like Isner's done makes Federer look bad