the 2016 pick won't be going anywhere.
It's only tradeable for a top 10-20 player. In fact I don't think Danny would even give it up for most players between #15 to #20 in the NBA (eg Love, DeRozan, Bosh etc) so that makes it really only up for trade for top 15 players.
Dwight won't be much. We can sign him when he opts out, and Morey knows this. Depends how serious the Rockets are on resigning him next season.
Gallo is probably similar value to Dwight, perhaps slightly less.
I think of all our assets to get both:
To Rockets:
2016 Dallas pick, 2018 Memphis pick, Amir Johnson, Jerebko.
To Celtics: Dwight Howard.
(wild card: Morey says Danny must take Ty Lawson for Lee's expiring).
To Nuggets:
2016 Celtics pick, 2016 Minny 2nd rounders, James Young, RJ Hunter
To Celtics:
Gallinari
Morey is probably asking Danny to take Ty Lawson for David Lee so he can clear cap room in Houston. Danny likes Ty a lot, and his salary is only one more season.
Still a lot of money for a trainwreck.
Worst case we could buy him out.