I'll definitely watch less when Nadal stops, but I still watched pretty much every match of the AO at night, fucking up my rhythm completely despite him being absent. So it's safe to say it won't end there for me.
I have to retract my earlier post. I probably won't stop watching tennis, but I do take a break from it if there is a boring tournament where none of my favorites are playing. There are really only one or two of those kinds of tournaments. It wasn't fun for a while, but it is just now becoming so again.
I don't believe I'll completely stop watching but I certainly won't be following it as closely after Fed retires -- unless someone with an interesting game comes along before then. I didn't watch as much during the Sampras era because I found his serve-put away domination pretty boring. And I've pretty much given up watching the WTA with the advent of Sharapova and co's annoying shrieking. So I guess I'll stop if, after Fed retires, the men start making long drawn out groans with each shot.