What ? Of course it reduces the chances of him leaving. It increases his value straight away. What clause are you going to put in his contract ? If it's a minimum release fee then it's still going to be more than if he didn't sign the contract...
They want £40m for him with 1 year left on his deal, how much do you think they ask once he signs a new deal ? a lot more... more than other clubs will probably be willing to pay.
Boohoo, hes got his own life to worry about... his job in life isn't to make Everton as much money as possible. If he wants to leave then he's well within his right to let his contract run down just as anyone in any profession is free to do so. It's only football where this is considered some appalling sin.... why ? because football fans are a precious bunch who struggle to have a rational thought process at the best of times.