Why trade Green ? He's just starting to get his game back, and his aggressiveness couldn't be better. He's learning who he needs to be, & has the right coach to put him in positions to succeed.
Keep him, keep Rondo, Ainge has already built a treasure chest of assets. No need to get more when you're a big man away from being a perennial playoff team.
Wait it out, and strike when that 5 man becomes available. When he arrives, you'll need the Rondo's and Green's right beside him. You have enough ammo in the tank that will allow you to bring in that big without giving up Rondo or Green.