No matter how happy he is he'll be off like a shot if the right offer comes in. Same as every other manager and player in the world.
Define that offer.
I can see him going to somewhere like Real Madrid for a couple of years (and lets face it, in common with most who go to manage there he'll get two to three years tops), but he won't have the level of control there that he has here so I suspect if that did happen then it would be after a prolonged period at Villa. To define that I'm thinking in the range 6 - 10 more years.
Could he go to international management? Maybe when he wants less intensity in his day-to-day, he might, although as a proud Basque, I can't see him taking on the Spain job.