Juventus have the leverage in Higuain-Chelsea deal right now. Higuain and Chelsea want eachother. If Chelsea want him now, we would have to pay to recall him, to make him available. We don't want to go through with this if it's not worth it when there is still another 10m left in the loan deal with Milan and the ability to sell him in the summer. If Milan buy the clause is for 40m, if he comes back and we sell to someone else it could be more than that. So Chelsea will need to make a deal that Juve will want to accept more than those possibilities.
I don't see Higuain going to Chelsea this window unless they offer 40+m for a purchase.