Giannis isn't going anywhere unless he demands it. You hope he stays forever and you get to retire his jersey as a forever-Buck. Considering Kareem hated Milwaukee and left, Giannis would be the Robin Yount and Hank Aaron of Bucks Basketball, which really needs a player like that.
We could probably get by fine with Giannis and Lillard as the only big scorers, but I find it hard to imagine Middleton and Lopez have any real trade value, and it's their two positions which need replacing more than anything. Middleton makes way too much for his production and Lopez is too slow to catch the cutter anymore. But good luck adding speed and defense basically without the draft.