I'd sell him to Chelsea for the right price, say £30m+ and if there are no significant bids from elsewhere.
He's 32 in the summer with 12 months left and as much as I love him, I don't think he'd do much for their game. I wouldn't hold it against him either.
Chelsea have turned into tight bastards though, they can't get anything over the line and I can't see them paying up anything near appealing enough for us to sell him to them.