Amalric comes across a bit like Robert Baratheon or a nicer Henry VIII and prone to obesity. As such I doubt he'll be good enough to hold off Saladin by himself. In concert with Richard I and Phillip II though they could maintain more of the Kingdom than OTL since I believe he'd be able to mediate/manipulate the Angevin-Capey rivalry to his advantage.
A longer life practically guarantees at least one more surviving child with Maria Comnena which will have interesting repercussions regardless of gender - a son could reign differently to Baldwin and have heirs, a daughter would bring a potential claim via her children to factor into regional politics.