There are speculations about Arsenal allowing Thomas Partey to leave this summer. Honestly I don't really have a problem with selling Partey at that amount. The problem is also selling Xhaka as well. It'll really leave their midfield lacking in experience though. In as much as I want him gone too but not on the back of losing two of their midfield generals at one go.
Remember that the midfield is at the heart of how they play. Even if the new guy comes in and hits the ground running, we can't realistically expect two new midfielders to hit it off immediately.