This is kind of an ironic question for me to answer considering how I just ended one of my fics, but, I'd have to say, yeah, given the assumption that Ash and May love each other, yes, Ash would give his life for her. Now as for sacrificing countries and possibly the whole world...well, I just don't know.
Considering the fact that he is willing to risk his life for his friends, it is almost completely likely that he would be willing to give up his life to save May's without hesitation if he truly loved her. How much would he be willing to sacrifice in the end though is a good question and one that is virtually impossible to answer.
"The hardest thing about dreaming about someone you love is to wake up but if the only place I could see you was in my dreams I would sleep forever"
Ash would turn to Pikachu and the ribbon for comfort while he remembers all the good times they had together. It would phase his goal to be the Pokemon Master for a short duration, but it will not stop him.
Yeah, well, Ash would be devastated by her death, and the details of said devastation have kinda been covered so...yeah.
Well, I have a new question. Suppose Ash and May were dating, but then broke up over something more or less trivial or stupid. If Ash caused the breakup, in what way would he go about trying to make it up to May so that they could get back together? If May caused the split, then how would she?
Personally I would like to see him do something like this song vid shows (not sing in an abandoned warehouse) but wait for May, I mean it is simple... like Ash. Even if he won't think it's romantic or anything, it would have the opposite effect.
That and I couldn't think of anything else
You're born, you take s-. You get out in the world, you take more s-. You climb a little higher, you take less s-. Till one day you're up in the rarefied atmosphere and you've forgotten what s- even looks like.
So, imagine Ash and May have been together as a couple for a good while, and Ash wants to tell May that he loves her. Again, they've been together for a while, but those three words haven't been said yet. How does he go about telling her? Or, if you want, you can reverse it as to how May would tell him.
Ash would take May to their favorite dating spot(if any). He lets her walk forward, and when her back is to him, he would embrace her from behind. Then he'd whisper in her ear those "three little words". May, who was at first taken aback by Ash's embrace, would soften up upon hearing the words.