I just have a lot of trouble grasping the idea that he has peaked. In a lot of ways he's just starting to realize his potential. That doesn't make him untouchable, but there surely is no rush to capitalize on his value.
At the same time, winning has increased the value of everyone on this team. It's not all about one guy. Masai needs to keep operating on his own terms and not do anything that strays from the bigger vision. The party that comes into negotiations without any signs of desperation usually gets what they want, and often a little bit more. As long as they keep moving foward, patiently, but with the big goal always in mind, then they will be far better off than letting circumstances determine everything by trying to guess where a certain player's peak value may or may not lie and depend on such guesses to guide their actions.