I think everybody will be happy if 2 things happen.
1. Brown and the Celts agree to a contract extension.
I don't believe Brown is a max player, so if Brown agrees to a 100m for 4 years deal, that's a good deal for the Celts.
2. Giving up Langford, instead of Brown, for Sabonis solves the Celts' problem of needing a quality big man.
Right now the Pacers don't have leverage because they're going to lose Sabonis for nothing once Sabonis becomes a RFA in the summer.
There will be a team out there that will offer Sabonis big money.
So I think the Celts can acquire Sabonis in a trade if Ainge is interested.