It's rare - but I remember P.J. Brown un-retiring and having a big role in the C's title, just by coming up big in a key spot or two. I think he came back a little sooner than this though to get back into game shape. Ray may be able to hit a big shot, but he also has to be able to guard at the other end if he's out there in late game pressure situations. Sometimes you can do offense/defense switches, but sometimes you can't.
Feels like this would be a weird way for Ray to retire, as opposed to having his last go-round knowing it's his last go-round. But that doesn't really matter in the big picture.