Why are things so black and white in here sometimes? He's coming of a knee injury. It takes a while to get back to fitness in cycling sometimes. Look at LeMond's 1987 and 1988 results (or lack thereof). He's 29. More than likely he'll be back to some kind of form. Knee injuries are particularly tricky. But it's very rare that riders can't make a full recovery (it does happen, though). He most likely won't come back to win Grand Tours, but I don't think that was ever in the cards for him, his own self-confidence notwithstanding.
I've seen no evidence that motivation is really an issue. Froome, Quintana, Contador all have their pet causes they support. Those haven't kept them from winning most recent GTs. But even if motivation is an issue, there have been many others who have seemed to have struggled with it as well: Visentini, Betancur, Cipollini, Lachlan Morton, to name a few, who have nonetheless either made a good hash of it or are still going strong.
I've seen no evidence that motivation is really an issue. Froome, Quintana, Contador all have their pet causes they support. Those haven't kept them from winning most recent GTs. But even if motivation is an issue, there have been many others who have seemed to have struggled with it as well: Visentini, Betancur, Cipollini, Lachlan Morton, to name a few, who have nonetheless either made a good hash of it or are still going strong.