Well since he's in the hospital for 5 weeks he will probably lose a decent amount of weight since his diet is more controlled there (unless people are bringing him food- I would ask everyone to NOT bring him food even if he asks).
If having a stroke can't make someone turn their life around then I don't know what WILL. All I can say is good luck and I hope when he gets out of the hospital he decides to get into shape so he'll be around for his family.
Have you spoken to his wife? What are her thoughts?
And if he does decide to change- I'd totally support him 100% of the way