For the weight issues, he has to work hard to lose that excess pounds. Still months to go, so again, this is doable and hopefully that stomach issue that he had before won't come out again. That is the main problem here as it is viral and come back anytime.
Training hard won't help and is not advisable. He should train-wise.
For me, no need for hard training as I'm sure there's no problem with his strength and body conditioning. His stamina is surely still on top and his quickness and speed are still the same. The problem lies within his inner body that he needs to work on.
You are correct, the condition is viral and can come back anytime. There's no 100% treatment but rather there's a 100% chance to avoid that.