Very odd, quite cynical decision to go now. In the summer, yes. Would make sense. But not with so few games to go and an 8 point lead. But as I said, in football, if you don't leave on your own terms, you're getting sacked at some point, in any case.
On the other hand - Gerrard now has a great chance to win a trophy at first time of asking, because unless they get Rafa in, Celtic's dominance of all competitions is probably over.