If Nonito Donaire won this fight and the team Inoue wants a rematch, they would need to do it quickly. Donaire is getting old, as much as I love the guy as a boxer, his age will be his biggest opponent. also, if he declines (which I think he won't) a rematch from Inoue if he ever won, I'm not gonna blame him.
We will have to see what the contract between the two says, since Inoue won the previous fight if he won again I do not think there is going got be a lot of interest from the fans in watching a third edition, however if the one that wins is Donaire then I think a rematch will be possible as everyone will want to watch a third fight, and since Donaire’s age is getting to the point in which his skills could decrease then I think he would be interested in fighting immediately as well, due to the money purse a third fight could bring to both fighters.
If Donaire wins the rematch may happen ASAP, likewise, age will really affects him much. Or his team can retire his gloves
with pride as a champion though I'm not buying the pride side since fighters nowadays are more into money, practically speaking
they will look for better paychecks instead of gaining that pride. But we never know, still depends from how this fight will end
and how both fighters will agree to whatever decision they might after.