Indeed Newcastle United's performance not quit well and drop to 8th standings position but difference with their striker Alexander Isak had impressive performance in this season after scoring 15 goals of 22 matches in Premier League. Its very good statistic and I think many teams interested for sign him on the next season, but Alexander Isaak keep loyal with Newcastle United and won't to play with other team until his contract expiry.
Newcastle United has opportunity without participants in European competition if failed to reach to six position standings, questionable for Alexander Isaak will stay with Newcastle United next season without playing in Champion League and Europe League or acceptable the interested team has chance for playing in champion league.
This happened because they were facing a storm of injuries to the core squad and even if it wasn't wrong they had lost almost 8 core players to injury at that time thus affecting the team's performance. Alexander Isak has had some good moments this season and he has been one of Newcastle's goal machines. Many clubs are starting to see his abilities, especially since he is still young enough to develop a career at a club that has far more potential to win titles because staying at Newcastle doesn't necessarily mean he can become champions.
His desire to stay until his contract ends there is still a chance for other clubs who are interested in signing him because even though he says so. If the club intends to sell because they need some additional players that will be another matter and maybe he will get a place as one of the players to be sold.