Excellent post.Exactly. Nadal still has a good 5 years left of good tennis, maybe not his prime, but he doesn't need to be anywhere near his best to sleepwalk to GS finals anyway. I'd pick him to win any GS no matter how terribly he is playing.
He has made 6 of the last 7 GS finals - it is pure stupidity to suggest he won't make 100% of the next 25 GS finals.
Now considering the worst case scenario that Djokovic (the only guy who can stop Nadal in a GS final) makes 25 of the next 25 GS finals as well, at worst, Nadal can win only half of those finals, meaning he ends his career with 22 - 23 slams.
At best, Nadal will win all 25 of those finals, and will end his career with 35 slams.
EDIT: sorry, got carried away and presumed Cinci would count as the 5th slam in a year.
Worst case scenario, Nadal ends with 20 slams (loses half of the next 20 GS finals to Djokovic), best case scenario he ends with 30 slams (wins all of his next 20 GS finals).
So you have Nadal pegged at hangin up his racket with between 20 to 35 slams. Good math, overall.