If no-one meets the price and he has to stay, I could see him signing a one year extension. He will want to up his wages as soon as he knows no-one will meet the asking price and I expect a lower than £100m release clause inserted, somewhere around £80m would be my guess.
He isn't going to sign a one year extension if he did it would have to be on the same terms you can't increase wages in an existing contract. If he signs a new contract, which doesn't seem likely, then it will be for another 5 or so years.
Forget all this about him losing out on wages . The sort of wage increase being talked about at Everton would be dwarfed by any signing on fee, share of transfer fee and increase he would be looking for at a CL club.