Of the big 3, having MIddleton sidelined with an injury is far less a problem than it is with either Holiday or Giannis out. With guys like Crowder, Ingles, Connaughton, and Allen available, there's a decent group of back up personnel that some of the slack is covered. It also increases the role of Portis, which isn't a bad thing either.
Hopefully that won't be the case. But, based on the recent history of Khris, it could well be that he spends some shelf time.
As far as his being with the Bucks next year, I think it's his choice. This article, from Forbes, tells a lot of interesting aspects about where this could go.
Milwaukee Bucks' All-Star Khris Middleton has four paths forward with his current contract situation.
www.forbes.com