Chopper will one day be able to cure any disease. Law is a doctor, he understands what great of a feat that would be. He understands that someone with that ability should be alive as long as possible, to do the maximum good. Also, I believe that Avalo Pizarro is both Chopper's future opponent and the former king of Law's homeland. Chopper will defeat him for Law. Chopper is the most naive and childlike Strawhat. A mature Chopper, after he lived 100 years, would be a stark contrast to him now. His mentor Kureha also is unnaturally youthful. Perhaps, if she got the same surgery performed, they could still work together in 200 years or something.

