I've had convos in the past with people about how Belichick would handle certain Celtics rosters. Given his philosophy of trading away guys a year too early versus a year too late, my guess is that after the 2010 finals loss against the Lakers, there's no way he would've brought that crew back.
Whether it be Ray Allen, Pierce, or KG, I'm convinced that if Belichick was running the Cs, one of them would've been traded way earlier than what ended up being.
My guess with Smart, yes he would probably frustrate Bill with his shot selection, but something tells me Smart would be a Belichick type of guy, specifically with his compete level and drive. So if Bill were here, I bet he'd do what Ainge is probably going to do too. He's gonna let Smart go to the market, see what he's worth, and if a team overpays him, then he lets him walk.