Next year is probably the first year where there's a reasonable chance that they won't. That said its still far more likely that one of them will still pick one up. Between age, injuries, and much more inconsistency from both of them (relative to their prime seasons) though they don't have long
what??? what is up with you guys, Federer has had just as solid as season as his last few, there are no real indications that much has changed from him. Nadal was having possibly the most successful season of any player on tour up until Wimbledon and his injury issues; his form obviously has not dissapeared but he has a temporary physical defect.
who knows, maybe the two won't play that well next season, but this season certainly is not any strong indicator of the two declining except possibly indicating that Nadal should make a more easy going schedule of tournaments to play.
I think they will probably each win one next year but then again who can predict such things reliably, this is one of the most unpredictable sports out there, despite the formality of the last # of seasons