It never really left Minnesota's hand, sure. But Cleveland was in a unique spot of their GM not really having the option of not getting the player, thus they had 0 leverage. That situation was fairly unique.
I dont see a team out there that MUST acquire Paul Millsap.
No, but there's probably about a dozen teams in the league whose profile would be seriously improved by acquiring Millsap in exchange for what they'd have to give up, including the Thunder, the Nuggets, the Raptors, the Wizards, the Rockets, the Hornets, the Pelicans, and so on and so forth.
I include the Celtics in that list, but as I said, I don't even think the Celtics should go after him because I'm not a believer in the Millsap/Horford frontcourt. But the team would definitely be better. I just don't think it addresses the rebounding issues sufficiently enough.
But Millsap is a seriously good player. And Atlanta will get good offers for him, as every team does when they're trading good players for reasons other than salary dumping purposes.