I could see Mercury being disillusioned with the X-Men in ways different from Surge or Hellion, depending on the HoX fallout. The senior X-Men finally drawing a line in the sand might appeal to Surge and Hellion, while at the same time it might seem to Mercury that the X-Men have finally lost the last of their heroic ideals and gone full isolationist. There's a lot of room to play with character POV given the set-up so far.