@Mikie as I've said elsewhere, my wife has had both knees replaced. Your doctor has to tell you that they won't last forever. They won't. But you'll get 20 or so years out of them, and at that point they'll have to be redone. Or you'll be dead by then.
If you keep hitting trees, well.....
You can keep riding. You'll have to deal with the reality that you don't have your own knees anymore. Cycling is better for your new knees than running or hiking, but it's not impact-free. Let no one blow sunshine up your skirt on this one. It's a limitation you'll have to deal with.
The best thing you can do is abide by the PT instructions and not fall off your bike afterward.