I don't care what money is being waved in front of us at the moment: if Alex wants to stay, then we should make absolutely sure that he stays.
If he decides that he wants to go, then by all means let's get as much money as we can for him - but if he decides that he'd prefer to develop his game in a great environment, and get lots of matches under his belt (rather than playing in a big club's reserves and/or warming their bench) then there cannot be any other thought in our minds than to keep a firm grip on his contract.
We don't need to sell. We shouldn't sell unless either we want to, or the player in question makes it clear he wants out. Simple as.