I don't think Osimhen would like to play for Galatasaray next season. It is quite bad for his career to play in the Turkish league really. Honestly I would like to see Osimhen playing in the Premier League.
If Galatasaray win the match in the derby tomorrow then I think they will most probably complete the league as the champions. If Galatasaray win a 9-point gap would be enough for them during the remainder of the league. If Fenerbahçe win they will drop the gap to 3 points. And as they are going to have an easier fixture than Galatasaray they would have a big advantage for the championship.

Wether Galatasaray wins their game against Fenerbahce on Monday or not, I still think that the reigning Turkish champions will still retain the league title this season. Unlike Fenerbahce who are still playing in the UEFA Europa League competition, Galatasaray have been eliminated from Europe so I expect them to fully focus on winning the league title this season.
Between Galatasaray and Fenerbahce on Monday, I expect a very tough and entertaining game between the top two sides in the Turkish Super Lig but if you ask me of my prediction of the game, I think the home team is going to snatch all three points from that game.