Our board have a few options.
They can sell him to Chelsea
They can let him finish his contract and let him go to Chelsea for no fee.
They can give him what he wants, which is presumably better players to play with, and more money.
Or sell him to another club, preferably in Europe.
Like you say, if it makes our board sit up and realise that doing the bare minimum, or less in the transfer market, means we lose our best players every season, then we might see both Sanchez and Ozil stay.
Personally I think he will leave and go to another top European club, while we can still get some money for him.
I also think he won't be replaced adequately.