That's not what they'll receive though. It's not about whether or not he's worth that, it's about If they want 75m for example, they will just set a 100m price. I just don't see them giving him up for 50 million (~75 million offer) as it's quetionable whether they would be able to properly replace him even if they use all of that money. While there are a lot of better players than him, Palace's list of possible targets would be way smaller than that of a top 6 club for example. And then there's the risk of his replacement flopping.
I may be wrong of course, I just don't see them being desperate enough for 50m to lose their best player and bother finding alternatives with all the risks involved. Unless, again, he tries to force a move.