Next stop not cancelled yet : Davis cup.
protected ranking is not used for the seedings
It's a minimum of six months without play, so if he doesn't play this year (only DC left he hasn't ruled out) then he can apply for protected ranking and thus be seeded third for his next nine tournaments or the next nine months, whichever occurs first.
; for the purpose of entering tournaments, it might only be useful to enter the summer American MS1000 tournaments if ever he fell down to number 50 in the world or something, which is extremely unlikely. Then no I don't think he will use it.
Besides, I don't think he will drop out of top-4 during next year. For the rankings after the Australian open when you take off all points until then, he's still number 4, 1055 points ahead of number 5 Ferrer. After Miami, the same : 1230 ahead of Ferrer. After Barcelona 120 points ahead of number 5 Ferrer, and that's the way to decide top-4 seeds for Madrid and Roma. His top-4 seed should not be in danger during clay season, first time it might be in danger would be ... in Roland-Garros, if he's very disappointing during clay season.
But we might have Nadal-Djokovic (and Nadal-Federer) semis in the first half of next year, that's the main change that we should see in the first part of next year.