I think Giannis signs some sort of extension but it might be something shorter and less than a long term max deal to get another bite of the apple in a couple of years when finances are more clear and stable.
In the meantime they need to do a better job of surrounding him with some complementary pieces. A young shooter at the "2" who's a decent defender would be my first pick-up. A point guard who's better at the pick and roll game would be a better fit for Giannis than Bledsoe who really doesn't seem to excel there. I'd be fine with moving on from Bledsoe though you might lose some defense in that swap.
If you have to trade Middleton then you do it. Hard to replace his production, but his "type" of guy is easier to find than maybe some others. Look at a guy like Jae Crowder, for example - very manageable contract, decent shooter and defender. (I believe he's also a F.A. so might be an option if you have to move Middleton?) If you can get more consistent production from your "1" and "2", you can deal with a little less from your "3".