I like Al Jefferson to play alongside KG. Rebounding and a prolific low post scorer? That would be just awesome to have despite his defensive woes, which I really have little worries about in all honesty.
KG doesn't stay if you get rid of PP, end of story, so what you suggest wouldn't be an option...
Paul Pierce is still with the Celtics last I saw. Also, KG has a no-trade contract, so that will still be hard to move regardless of Pierce being here or no.
And believe me when I say, even if Pierce is not here, while Ainge remains here, his interest will still be to compete. So the key here is moving KG, not whether Pierce is here or not.
If KG isn't here, I don't want Josh Smith, or Al Jefferson for that matter. Their salary cap space is better used elsewhere.