A lot of this is a broader question too. We have an aversion as a fanbase to selling our best players. I'd say there are a number of reasons for this- we have a bit of a chip on our shoulder as a fanbase, we have had to move a lot of (particularly younger) players well before we were ready too, and it kind of underlined in quite an acute manner that we are not a big club (and at times through the 90's were a financial mess).
However the clubs we are trying to emulate, Dortmund, Sevilla, Leverkusen to a degree Leicester all have a very different attitudes to selling players. It provides a liquidity in to the club, helps with FFP and allows to bring more through. While we don't want to lose players, we should be a bit more open to it. It doesn't meant sell to buy, or that we are going backwasrds or we lack ambition or whatever. If the price was right, I can see a lot of sense in selling 2 of Kean, Calvert Lewin & Richarlison and making 1 of them the key man. King could be backup and you could easily pick up a Danny Ings type to provide some competition too.
With the funds raised we could quite easily go and pick up a Bissouma, Pedro Neves/Raphina, Max Aarons at right back or players of that nature in 3 key positions we need more players. None of them are massively, all of them are young enough that they should get better and have good experience in the league so are unlikely to flop.