If Gaballo defeats Donaire, I don't think any champion will have the interest to fight Donaire anymore.
Donaire will retire if Gaballo beats him. How can he face another champion if can't beat a young boxer anymore?
It's finally over for Donaire if he gets beaten by Gaballo in this upcoming fight because no one will gonna risk their belt just to fight someone who does not currently have anything in his pocket anymore. Champions will only fight a proven boxer at this point or someone who is also a champion like him. If he can win this fight somehow, then it would be good for him if they give him another chance to fight Inoue or someone at his level in their current weight division.
Better to follow what Manny did after losing his last fight to Ugas.
Even inside their mind, they think they can still fight and win, but the body was aging and most of those movements are no longer the same.
Best to enjoy life after retiring. He doesn't need to prove anything if ever he loses the fight. Fans will always remember him as one of the best fighter
on his generation.