OK Jons voice ain't the same as for 10 years ago, is it not normally???? But think they will keep together as a band for a long time, maybe with Richie singing some off the songs...
I'm sure that Richie will keep on making music till he can't play his guitar anymore, maybe he will make some more solo stuff, or join up with other musicians.
Jon will make some more movies, and if there comes a time where Bon Jovi will stop, Jon will not make a solo career.
Tico and Dave are still fresh, so the only problem in Bon Jovi is Jon's voice, and the problem ain't that big, i think Bon Jovi will keep on for another 20 years (If we will still have this kind of music at that time)