Honestly doubt he even leaves. Chelsea have too much pride to sell at a price low enough to be acceptable to buyers. Seems to be the same with Mount. Mad asking prices for players with anything but impressive seasons behind them.
His wages are almost as bad as the fee demands. 250k p/w for a rehabilitation project would be ridiculous. Seems like there would need to be major concessions from both Chelsea and Havertz for this to be a possibility.