I've been reading that slowing down from aging will affect his performances greatly. He relies plenty on speed, but he also has a sturdy chin and decent power to fall back on. If worst comes to worst, he could just move back down to 140, when his speed and legs can no longer protect him against the bigger guys at 147, to slug it out with guys his size.
He depends very much on fast combo punching, exploring angles while he unleashes series of power punches and he is very, xtremelly dependant of footwork and fast legs to move in and out - that last item is the key factor for his defense and offense. GGoing down to 140 pounds should make him not so dependedt on mobility and he can stay and go for it more at ease.
I don't think he will go down to 140 if he loses his speed. After all big fights (or most of them) are made there would be no point for him to keep fighting. Defending title multiple times is just not his style. Probably in 2-3 years he will quit boxing and sacrifice himself completely into politics as there would be nothing more in boxing for him. With exception of maybe fighting FMJ