It wouldn't be the worst thing to sell him. His fee is already covered by the Ndiaye sale, so we're pretty much at net zero with him. If we did get £22mil then that's a healthy wad of cash for the summer and good profit after an awful season, even if we do get it over 3 seasons. He's too good for the Championship and has nothing left to prove at this level. We'd be holding his career back. I have no problems with players leaving for the right reasons and for the right price. Hamer's goals and assists last season were very good for the team he was playing for and he contributed to the lion's share of them, 12 contributions from the 35 goals we scored. He'd be a steal for any newly promoted club, or an established lower half team.
I've posted elsewhere that I'd be more worried about what Wilder would do with £22mil. Buy 8 average players or buy 3-4 quality players with potential resale value in a season or two's time. I'd rather see quality over quantity, and not sign loads of average players out of panic and desperation.
We need to stop viewing player sales as evil and view them like Brentford and Brighton do, a means to strengthen and push on. The sales only annoy me when the money dissappears, which in fairness the Ndiaye and Berge money never did, as they paid for Hamer, Souza (okay, bad example), and Archer.