He isn’t going to sign an extension this summer, and its possible he doesn’t sign one next summer either, making him a FA in summer of 2024. You could trade him that trade deadline of Feb 2024 but you aren’t going to get value you could now. So it will come down to how confident is Brad Stevens and the FO that after years of being in these kind of trade rumors that Brown wants to be here long term.
For me, I would trade him if I also got to keep Marcus Smart. Championship windows can close super fast, so with the roster they have, I go all in. Brown is a really good player, but if you sub him out for Durant and asked me which version of the team had the best chance to win the title next year, I would pick the Durant Celtics every time. If Brown and Smart had to go, then I probably dont do it unless the Nets throw in another player