He'll still own Federer everytime he plays him there. Plus, in alot of people's eyes, he's already the clay GOAT.. 81 match winning streak, 11 clay MS series, 4 consec French Opens and only 23.
Borg wasn't undefeated at RG so why should Rafa have to be? He actually lost twice in at RG and didn't play one year. He's also played it 8 times, Rafa only 5.. We'll just have to see.. but in my opinion, Rafa's clay court credentials have no where to go but up. He's pretty much proved all he needs to in the eyes of most tennis fans and professionals.
But he is not the clay court GOAT. To say he is better then Borg on clay already is just rediculous.