CAMELOT FANTASIES

Well said again Lady TT, and General Hercules what more can I say?

Well, I don't think anyone is really mentioning it, but I think Rafa's back or shoulder must clearly be affecting him.

He was just serving powder puff serves to Nishikori, who was playing like Davydenko of old played Rafa on hard courts. Taking the ball early and hitting with sharp angles and not giving Rafa time to set up anything.

He has almost no power on serve and has lost significant power on his forehand.
This is indicative of either a complete loss of fitness, or injury.

Fitness can be fixed.  Work very hard and it will return.
Injury on the other hand, you either play through it at reduced capacity or take the time off to heal.
With injury, you can't put in the hard work, or you risk further injury.
So based on what I've seen, I think he has been playing at reduced capacity due to injury.
Otherwise he would be more fit.

If injury is indeed the case, I think I would not play past the US Open, maybe not even play there.
He should take the time off to heal as well as possible, then return to training on clay, working as hard on his fitness as his body will allow.

He basically has no points to lose this year anyway.  Playing more only risks additional injury or aggravating whatever he has.

I would use the proven strategy of 2012-2013. Take the months off to heal injury, then work on fitness, and come back strong.
He will be rusty at first. So skip the Australian Open, and return on minor tournaments on clay in South America, and build match play and confidence just as he did in 2013. 

With this strategy, I think he can get back to the high level necessary for him to compete against the top players at Roland Garros and elsewhere. If he can dedicate himself to doing this, I wouldn't be surprised to see another couple of majors from him.

If that's what he wants, of course.  At some point, players do get sick and tired of fighting injury, having to get fit, the whole cycle, and call it quits.

I don't know if he has more desire in him to do more, or not, only he can answer that question.

Respectfully,
masterclass