Just from casual observation and anecdotally, ET and CBS seem pretty tight.
From ET being at Summer League with Stevens and his son to their (ET and Stevens) trip to Africa together, to articles like this (
http://www.masslive.com/celtics/index.ssf/2015/04/boston_celtics_notes_evan_turn_4.html) during the season, there seems to be a pretty strong connection there.
Also, it could be argued that ET's successes with the Cs this year are a testament to CBS. ET, the reclamation project, is as much attributable to CBS as it was to Ainge and even ET.
Ultimately, it's going to be ET's versatility, a trait with which CBS is generally enamored, that will keep him here longer than some think.