Diego Sanchez's video on what happened. Basically the UFC wanted him to sign a paper before his last contracted fight that would prevent Diego from ever being able to be compensated if he were to suffer from longterm damage from all the fights while employed by the UFC.
For the UFC to demand he sign that paper before his last fight should make you wonder do they have medical papers that show Diego has some brain damage? What you should be asking has every UFC fighter on the last fight had to sign that paper? Is the UFC trying to avoid paying out big money to fighters that have been true warriors in slugfests in the cage that end up getting CTE and are unable to care for themselves 5 - 10 years after they left the sport?