The lad is just 25. Perhaps you know something the world at large is ignorant about? Is he about to retire?
The way I see it, Federer is soon out. That leaves Andy at, say 27, with a a few more years in the game with a clearer shot at finals. No reason at all he cannot capitalise on one of those that happen to be slams.
Whilst I can see sense in the theory that Andy may get lucky and win a slam by virtue of default once the other top players get too old/injured etc (what a thing to pin your hopes on) , I still tend to think he would choke in a slam final against a lower seed. Plus, there are, and will be more younger players on the scene able to push him further down the rankings.
At 25 he's done all his developing, all I see added to his game in the last couple seasons is more injury prone, and an even bigger self defeating chip on the shoulder.
HF, i'd be happy to wager a crisp scottish £20 note with you that he will never win a slam at any age.
My spidey sense tells me he'll be world #5 or lower within next 12-18 months, maybe sooner