Doesn't make sense for either side.
Lakers are actually in a pretty good spot - the only player under contract beyond this season is Nash. They will have tons have cap even if they resign Bryant, plus they're poised to have a decent draft pick in a loaded draft. Losing D12 is a blow, but they're poised to bounce back fairly quickly. No need to take on Bass who is under contract beyond this season and eat into their projected cap space.
For the Celtics, we're rebuilding. Its shortsighted and careless give up a 1st rounder for a 30+ year old player on an expiring deal. Might as well just kept Pierce. Especially if you're objective is to miss the playoffs for the lottery. If we trade any firsts, it will be in a package for a young player who will be part of the rebuild.