I would NOT blow it up.
Milwaukee remind me of the Dallas Maverics circa 2008-10. It looked like their window had permanently closed to. Dirk was still doing his thing much like Giannis is now. However, the rest of their team was a slow aging bunch. Kidd was no longer the star he was. Dampier was slow. Josh Howard was starting to have severe injury problems. Caron Butler had not worked out.
Yet, they stuck with it. Made a few changes and managed to break through from a low to mid level playoff team (much like Milwaukee now) to a title winner. The addition of Tyson Chandler changed everything for them. They got Shawn Marion. Picked up DeShawn Stevenson. Brendan Haywood for big man depth to replace DeSagana Diop who was a major loss for their defense (it would fall apart whenever Dampier sat much like the B Lopez now).
Milwaukee has done the most difficult part. They have the top end of their roster in place to win a title. Giannis and Lillard. The problem is their supporting cast. They have no terrible perimeter defense and little depth. Those are fixable problems. It will be hard as they do not have much trade assets but it is doable. They should not walk away from a team that could get back to title contention with role player adjustments.
They need to move on from Middleton. Acquire two quality wing defenders. Maybe offer up Portis for one of those slots. And they will be a force to be reckoned with once again.
I agree. They do need a new coach though. Rivers was a terrible and ridiculous hire. It's almost impossible to get a package back that resembles the value of a superstar. Guys like Bridges already cost 5 first round picks. On top of that, the picks will almost all be late firsts since the acquiring team is going to be really good. Thus you don't want to trade Antetokounmpo unless there's no other option.
Besides that, your other star Lillard may be at an alltime low in terms of trading value. You'd at least want a potential All Star in return, but your negotiating position is weak. Other useful players (Lopez, Middleton, Portis) are mostly old. They will not be attractive targets for teams with young assets. The best trades you can make here is fill a specific need for another contender and gain a specific need that the other team has in abundance.
The Bucks do need to hurry though. Their window, if still open, is short. In four years there won't be much left of Lillard and Antetokounmpo.
In the case that Antetokounmpo will be traded it would only be logical that OKC is his destination. And that would be really scary. The Thunder are already our most dangerous adversary.