I really want him to stay but he also needs to accept a lesser role. His body needs more rest at his age.
Really, this is silly talk. A player needs as much rest as the player needs. A player should play any role that a manager sees fit to play him. It's not like Xavi is a box-to-box hard-tackling player who throws his body around all game long. Most of a game for Xavi is basically going out for a jog- on grass. The largest stress for him is on his calves/Achilles because of the amount of bouncing on his toes he does to be prepared to receive passes (like a tennis player waiting for a serve). With proper stretching, care, and the *appropriate* rest, he appears to have gotten that under control.
As you get older, your tissue doesn't heal or recover as quickly, but, unless one is injured, one game a week the tempo Xavi plays isn't a problem. If anything, it's the training days right after the games where Xavi should rest more than younger players.