When the Cavaliers made the trade that sent away Kyrie Irving to Boston, the most critical element of the deal was the insurance policy the team got from the Celtics: the rights to the Nets’ top pick in the 2018 NBA Draft, projected at the time to be a top-five choice in a draft that could feature a handful of franchise cornerstones. Nearly two months into the season, circumstances have changed for the Cavaliers, but according to league executives, one thing that has not changed has been Cleveland’s unwillingness to part with that Nets’ pick, even as Brooklyn has exceeded expectations, thus dinging the value of the pick.