I'm going to be brutally honest and you might not like it.
Chelsea would mad to sell him. He's better than Rudiger, David Luiz is 32, and Zouma would make a natural partner for Christensen as they both mature. Why would you sell someone with so much experience in the Prem without giving them a proper chance in your first team?
I think he's better than Mina too, who I'm far from convinced will make it here, and missing out on Zouma would set us back massively with the disruption it'd cause to what's become quite a settled defence.
In short, we are in big, big trouble.
That's just my opinion though, and as always you can take it or leave it.