With that kind of defeatist attitude Crystal Palace would have sold Zaha a long time ago and then got relegated. MP is under a long term contract, we don’t have to sell.
Palace are still in the PL we wont be. To most players PL is second only in attraction to Champions League. Palace are way too reliant on Zaha much as Villa are with Grealish. It isnt good for them, both clubs can barely win a game without their star man. You never build a team around one man.
Put yourself in Pereira's shoes. You are going to want to be in the PL surely?
Losing him wont be a disaster, it brings in, relatively speaking, a huge amount of money to add to the pot already gained from being in the PL, to strengthen the team / squad over all.
We should never be afraid to sell any player, there are other players available to us all over the world.