He admires a lot Bob Dylan, who is still touring after 70's, and others like Gilmour, Waters, even Clapton still play at 70's and after... Clapton less, due to his health problems.
I guess He would still tour after his 70's, but maybe shorter. Guy uses to say that they are carried on a magic carpet on tour, so the only thing they have to do if MK still wants to tour is just do one or two big cities per countries, and do the countries where the usually sell more tickets.
As long as he still wants to record and play, he will. I´m sure, and he will accomodate to whatever his health is at the moment.