The OP might be a little hyperbolic, but we all understand there is a possibility it's not far off the mark right?
I'm not saying it is - but if he didn't ever come back to his level it wouldn't be completely shocking would it? I know there is a lot of fearful leading to wishful thinking on this one but we all understand he's not only going to not be running at "WR threat every race" level forever, there will be a point where his body just says enough and he will retire right?
For all intents and purposes he just missed an entire season with injury. And he valiantly showed up for the worlds (maybe for contractual reasons which is understandable) but clearly was competitively fit by his high standards. At 25 years of age that not a great situation and it's easy to forget this isn't a "Yared Nuguse completely undertrained until his 20's" situation - this guy has basically been focussed and prepping like a pro athlete since he was 16. Sure at this age the workload and intensity is lower because it simply has to be, but who is to say that intense workload on your body at age 16 is any different to intense workload on your body at ages 23-24 in a relative sense with respect to your bodies career capacity?
We know how he trains. Sure he doesn't do many, if any, heavy anaerobic sessions but the flip-side of that is that he does a mammoth amount of volume at still a very high intensity. Now if you logically think he wants to move more to the 5000m side of things and look at that WR, that's even more worrisome when you think of how he wants to get there. Because it's not great when you think of a guy developing a pattern of achilles injuries know the volume and intensity of training his mind and drive want him to do.
I've always said that every top athlete, no matter what distance, has a 4-5 year window MAX where there are really in their career best form. It's not unreasonable to think this was either the 3rd or 4th year of that window for him, and it was a lost season. Not only was he clearly not in his best shape in Tokyo I agree he just looked old. He was noticeably thinner and just looked pale out there - he didn't look healthy at all.
We also don't know what he mental state of mind is. He's married now and a dad. Loves his cars, has other interests. Made a ton of cash and will do so at least until LA no matter what. Maybe he has changed - he's still just a kid growing into an adult. I do think he will be back but it's not as cut-and-dried as I think people are desperate to believe it is.