They will die. You will miss them. And you will go on, just as they have, assuming their parents have passed, and just as their parents did, and so on. It seems worse than it really is. Grief is natural, and feels awful, but it doesn't kill you unless you exaggerate its effect on you. Some of us do this, and that's when we get a chronic anxiety disorder. If you have this problem regularly, I'd get into therapy and work on changing the way you think about things. A little spiritual help such as meditation might help as well to help you focus on the present, not the future -- life's hard enough without worrying about what hasn't happened yet.
You will be ok. My dad got diagnosed with Parkninsons right around your age, and I lost alot of who I was. I became a shell, but I now I realize that we Lose people. It's a hard pill to swallow, but at least you realize this now. Go on with your life and do the best you can for them. And cherish it as much as you can.
Hi, I am a fellow Chinese. I know words are always easier said than done, but please remember this: live your life happily and have wonderful memories with your parents. So no matter what happens in the future, you will always have those things to cherish and not just 空烦恼.