Sorry to hear that. I can relate though. My physician has told me that by the time I'm around 50, I will be "begging" for surgery for both my knees. He's informed me that I will be needing knee replacement surgery on both of mine and that I should no longer be active in any of the "physical" activites that I have grown to love throughout my life.
I'm still very active in the Martial Arts, my focus now though is on teaching and sharing with my students the knowledge that I've acquired over my 25 years in the Martial Arts. Not as much hardcore training and competition is all. I still do though, just not as often.
There's not alot you can do if you injure something like a knee. I know, I've blown both of mine away. Several times. No matter how good you take care of yourself, sometimes things happen that are beyond your control and your body wears out.
Now the decision is yours, how active do you stay? Do you change styles? Even if you change styles to something that doesn't involve as much kicking, there's always going to be risks for further injury.
I wish I had the answer to that for you and I could just say "here it is". Unfortunately, I don't. Do I dwell on the fact that I may re-injure myself further when I'm training and teaching? No. But that's me and my decision.
Ultimately, you should weigh the risks and if your love for what you do is worth it. I have come to love it so much that I continue to take the risks. Am I stupid for doing this? Many of my family members and friends would say "Yes" and have told me so. Maybe I am.
Again, my focus now is more on teaching, not competition and hardcore training, as it used to be. I haven't competed now in around 4 years. Do I miss it? YES!! I've always been a competitor and loved the challenge. However, I have come to the realization though, that I have nothing to prove to anyone or myself when it comes to my skills in the ring anymore. I know what I'm capable of, and now I try to help instill this into my students and live through their accomplishments and know that I helped them grow into that Martial Artist and person.
I do have one quote that I tell myself all the time and I heard somewhere over the years.
"Pain is just weakness leaving the body".