That's a tough one to call. I've seen bands the last few years that are a 'lite' version of what they once were, but I don't know if I'd say they should retire.
I would agree with 'the stones' they should have retired back inb the 70's when keith first died. How long has he been dead now, or does he just look like the crypt keeper???
Elton John used to be a great musician, now I'm not sure what he is doing?!?
It seems like there's a lot of bands that put out LPs/CDs just to prove they've got nothing left to say.
As reinforcement for that thought, I read an interview with Kerry Livgren (currently with Proto-Kaw) who when asked if he would ever record with Kansas again replied, "Why, what do they have left to say?" Amen Kerry!