Barring a major disaster, Nadal should easily get another six slams. We know how effective he is at the French, and really, the tournament is his to lose.
The thing that's being overlooked is: if Nadal plays at an 'average' level (for him), he is always going to be the heavy favorite at Wimbledon as well. How many times in a lifetime can Rosol show up? I'd argue once. Nadal owns Federer, especially an aging Federer. Djokovic is unlikely to repeat his grass success. Murray cannot stop Nadal at Wimbledon as he has proven time and time again.
And he's not exactly a mug at the USO and, especially, the AO either.
Nadal needn't win any slams this year to reach 17 before his career ends - he has plenty of time, there is no need to panic.
The only thing that could complicate Nadal's life is if Federer significantly moves the goalpoasts by winning, say, 5 more slams. Anything less than that and Nadal will end his career with more.