With current roster they have I don't think they need Giannis on their team.
I guess what they need is good rotation since they already have good shot to win a championship this season. If it happen that they trade their young valuable piece its like they are risking their future. Knowing KD he usually leave especially if he think that he's on losing team. So best to retain everyone and focus on their development. Let KD lead them and they might get good experience from a veteran star like him.
Agree to that, knowing KD better not to take that risk as he can easily decide to leave if he thinks that there's no chance of winning, just look on how he abanoned both Nets and Suns, after these two squads brings him to have that chance but did not materialize, now, we again see another transfer and this time to a much younger team who shows decent performance last season, a matter on how the management especially the mentor who will guide them together.