Take a year off to heal his body and get his mind together, work on his boxing (if he's gonna end up just swinging after the first or second round anyways, he'd might as well have improved boxing mechanics), and maybe do some S&C. There's way more to what your training camp is like than just who you're training with; if traveling abroad for several months and training with people that he doesn't know (it can take months, and sometimes it's all in vain, to foster the kinds of relationships where you're truly comfortable around the people you train with to allow them to push yourself beyond where you think you can go in order to improve) makes Shogun psychologically uncomfortable compared to just having his own little team, then it's very likely it wouldn't help him as much as you'd think, much less enough to start another career resurgence. Fighting is way more mental and psychological than people give it credit for, and if you're not psychologically there, it doesn't matter how physically there you are. He should probably bring in some more people to his team, though.
Shogun's way too big for 185, to the point where to drop down to MW he'd have to completely change his body type (lose some of his muscle, mainly; that little bit of fat around his stomach isn't gonna make a difference in dropping down a weight class), and I highly doubt that doing those things would help him in any major way. I mean, it might, but I'm not a nutritionist and I don't know Shogun's diet or what his body chemistry's like, but knowing what I do know about him, I can't safely assume that it would help him.