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.
Expanding the rumor, where do you think Isak would go if Newcastle successfully acquires Jackson from Chelsea? Isak's contribution to Newcastle has been significant during his time at the club, and if Isak's departure were to materialize, I'd prefer him to be at a club much stronger than Newcastle. A player of Isak's age, there are certainly still several teams interested in him if Newcastle gives him the green light to make things happen.