Isak won't make official statement about leaving Newcastle until his current club will able to find his replacement. However, he's in stance to leave from the club. I saw the latest rumor says his club targets Jackson as his replacement, but still waiting for more concrete news to come. If his club successfully sign Jackson from Chelsea, he can leave.
He can only leave in two cases: if Newcastle allow it (on terms Newcastle agree) or if he pays a release clause to end his contract early. What he wants or doesn't want, or whether Newcastle signs someone or not is irrelevant. Isak has a contract until 2028, so he is obliged to fulfill it or come to an agreement with Newcastle. As I understand it, now all interested parties are waiting, but Newcastle is in a better position because even if Isak's transfer does not happen, they are satisfied with it.
I am sure that Newcastle wouldn't want a player who hates them for not letting him go. Why would they play a player who will not play for them, that would hurt the team. So they will definitely sell him this year, only difference is that, they will not be blackmailed just because they want to get rid of the player. It means that they are going to end up with selling him for a fair price, not for zero.
It's true that we are going to reach a level where it would not be a weird one, it was a decent one, but that doesn't mean it is going to be something we can definitely handle in a way that would look to be fair price. So we need to reach it to a good level in order to make some good return for Newcastle so they can replace him.