Personally I'd keep him regardless - train with the U23's until he calms down and then he can start fighting for his spot again. If Pope get's injured or a red card we are in deep doo doo! rather a short term pain in the arse problem player than a debilitating situation like having Darlow or Gillespie in net.
Dubs is pretty simple. We've gone and got a better keeper as we needed to (I know many on here disagreed with that but I think its pretty clear now having seen Pope operate that Eddie is right), but he's probably too good to sit on a bench in that he's good enough for bottom half PL sides. So I could see the sense in him wanting to leave. Why he is going to another club to sit on the bench is a bit bewildering and seems like he is being badly advised by someone. Bottom line is though, we don't need to keep unhappy players. I like the Pep approach, if you wanna go, go. Toxic players are far worse than any benefits gained by keeping them around. I think Dubs is professional and wouldn't cause mayhem but how you handle these situations has a direct impact on players wanting to join your club. It is better to be seen as a club that gives a **** about the individual as well as the collective. There is a human aspect to football transfers. I do think Darlow is a risk though as a No.2 - I expected him to move on.