With how little damage he's taken, the fact that he's being selective about fights and not going 3x/year, and the fact that he's not all that reliant on youthful athleticism (quickness/explosiveness), he can probably go almost another 10 years of high-level fighting.
I don't see what you're seeing on the mental side. He might have problems in his personal life, but I see no problems with his fight mentality. It's actually one of his biggest strengths. He's not scared to fight. He's not scared of challenges. He usually has great game plans and he's good at executing them. He doesn't buckle when the going gets tough in the octagon. What are you seeing that makes you doubt he can stay in the fight game mentally? Fighting actually seems to be the thing that keeps him in order, to some degree.