When it comes to experience, I would say that Donaire would definitely dominate the ring, age might caught up to him, but, he would still find a way to show Santiago that he definitely deserved that title. But, if Donaire would be defeated, there is a higher chance that that would be his last battle, I think.
retiring had been called for how many times in this thread yet Donaire team itself had not mentioned about this for long so I think let us not tackle this because it is far from the topic.
If Donaire would not retire after he is defeated, I think that it would have a hard time getting the title back as his.
it is not about the title actually , for me this is how a true boxer do , to fight as long as they can (belt/title is just a bonus) so no matter or how long it would take? this boxer will fight till his knee stopped him from doing such.