The deal i see kings making with us would be:
Bradley, Bass or Sullinger, Pierce and a 1st round pick
for
Evans , Robinson , Salmons and 2nd round pick
The celts starting lineup would be then
Robinson, KG, Salmons, Evans and Rondo
Kings lineup
Cousins, Thompson, Pierce, Bradley, Fredette
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Kings in an instance get a whole lot better. Pierce would provide them with the winning pedigree the team never had before. Plus he gets to play out his last years in the westcoast. Bradley, Sullinger and 1st round pick is a nice insurance in case Pierce gets injured or only gives you a few years of service. Fredette can finally have a chance to have full pg duties.
Celtics get a whole lot interesting. Evans can play his natural guard/sf position. Imo he has been getting injured these few years because he is asked to do too much. Unfortunately he is not a franchise player nor is he a true pg. I think he can co exist with Rondo , get less injured and play alot better with a vet team. He is still very young, and Ainge was trying hard a few years to grab him. Robinson thus far is not looking like a great pick for the kings. They already have Cousins and Thompson upfront and Robinson is not getting a chance to warm up imo. The guy is definitely starting material and would be a nice upgrade to sullinger. While Sullies iq and maturity is possibly higher, Robinson has a good inch adv in height, better body, athleticism and quickness. With confidence he can be a monster
I'd hate to give up Bradley the most, but there are huge concerns about his shoulders. Its no worse than Evans injury concerns.
Overall i would think hard about making the trade. I don't think its wise to have , two aging players like kg and pierce in the lineup , stay competitive, lose them due to injury/age/retirement and dangerously start a drastic rebuild path.