It could well be that he just plain refused to be the one at the helm when Messi walked. He'd be remembered forever for that. Not that he's going to be fondly remembered at all by Barca fans I'd imagine.
That said, Messi has to be clear anyway. If he's coming he says so by January. If he wavers, even for a second, then we can't afford to linger and must move on. In my opinion we should be after another striker as a priority anyway, if Messi comes great but don't count on it.
For my money he'll stay, his family don't want to move. Unless the new guy doesn't want him.