I think right now even if Nadal was mentally at his strongest, he'd just be incapable of winning a Slam. He isn't physically ready. To me it's that simple. Now unfortunately, that also impacts the rest of his game and so it means he has many things to fix right now, but perhaps just being physically ready will put everything else in its place in double-quick time. On the other hand, the damage that has filtered down to his psyche might be unrecoverable even if he finds his fitness. Hard to say.
I agree, but I am offering (and endorsing) the premise that he cannot recover his peak physical form/fitness due to age.
Knowing that he can't do that will continuously bring his mentality down. Rafa's game was always about outlasting, and now he can't do that. As he ages, he will need to keep points shorter, which isn't exactly helping Fed hang with the younger, fitter top dog.
I see Nadal's situation a lot like Roddick's. Even when Roddick was in his mid 20s, a lot of observers were concerned that his body would break down early because of the wrenching style and his appetite for anti-inflammatories. And obviously that's what happened. I think it's happening to Rafa too.