What happens if I have to get my meniscus removed?

Arthritis. The meniscus acts as the cushion/shock absorber in the knee. When all or part of it has to be removed, the cartilage and bone see more stress over time and degrade faster - arthritis. However, leaving a torn meniscus and not taking it out can cause more stress as a flap can rub raw the cartilage much faster than having less meniscus.
Pain goes away. Your pain or mechanical symptoms should go away. Long term health of your knee may or may not be affected, depending on how much is removed, and on other factors inside the knee joint. When its torn , it's not doing its job anyway.