Top 4 should be top 4 even with NAdal and his limited schedule or Roger declining + he will have limited schedule probably by himself
than 5-8 should be the same , big hitters Delpo,Berdych and Tsonga if healthy are better than the rest the biggest threats for top 4 at slams and Masters1000. Ferrer will probably decline little bit - i mean he is not getting any younger, but thanks to his seedings he will be making QF, at many big events + points from Acapulco, and some 250 will be enough for him to end top 8 again.
Than 9-10 this is big question, basically anyone in top 20 with good season and form can go there, Tipsy was solid 2 years in top 10, he can do it again, but we will see, Isner,Raonic have potential to by YE top 10, guys like Wawrinka, Gasquet, Cilic,Almagro, Nishikori and other top 20 with can end up bottom top 10 too.
So i just can say top 8 if healthy should be big 4 + Delpo,Berdych,Tsonga, Ferrer
9-10 is really open for at least 10-15 players we will see who will have better and who much better 2013 than 2012 from those guys.