Whether Bird is out or not, there's no urgent need to sign a free agent. Boston has outstanding depth, especially at the wing and ball-handler positions. Jabari has upside, something that you couldn't say for Nick Young, Brewer, Sessions, Jack, and the others in the OP. (Same for Luol Deng.)
If Bird is gone, don't fill the spot. Boston already has a minutes crunch, with deserving players expecting to play short minutes or not to get into games.