Just because he told you a purpose for a doctor's appointment doesn't mean he told you the whole purpose. Or all the circumstances.
For example, he could be going in to have a hemorrhoid banded. I can tell you that after that, band practices aren't on the agenda. Or maybe he gets so nervous that he's going to be full of tranquilizers and his wife's going to have to take him home and pour him out of the car.
Honestly, if you're over 70 and still getting torqued up over this stuff, and your name isn't Buddy Rich or Tommy Dorsey, and you're not playing for 6 figures, I think you ought to re-evaluate just how tightly you want to be wound about this part time hobby weekend warrior band.