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.
Would Partey feel threatened by his regular position if Declan Rice joined Arsenal? I think maybe that's what Partey is thinking if the reason he left was in the summer and it's no wonder because Partey is actually a good defensive midfielder and thanks to him over the past season Arsenal's defense has been very strong. But again, every player certainly wants more playing minutes and doesn't want to just be on the bench. I think even if he leaves Arsenal it seems that Partey will still be at an EPL club and if this happens then Arsenal will lose one of the most important figures so far.