As a guess , Pierce will most likely remain, not because DA won't try and find something that helps the Celtics. I think Danny will explore his options.
With KG we still have a team even without Pierce, because we have Green. With no KG , the Celtics are lottery team. , even with Pierce.
KG may realize Pierce an't up to snuff , or is retiring, or is gonna be traded . For some reason KG's mind seems more open to playing with no Pierce .
I bet Pierce comes back, but you never know. Danny may be willing to take less for him than he was looking for Pierce sure ended the season on a awful note.