During the dead ball prior to the FT, there is NO RULE whatsoever which prohibits the player from leaving the floor. 9-3-3 is for leaving during a live ball.
If the player does depart during the FT, he could be penalized under 9-3-3. The ball would become dead immediately, even if the try were in flight, due to this specific violation. Therefore, the FT would be cancelled and the 2nd FT would be attempted if the situation involved a 2 shot foul or the opponent would be awarded the ball OOB at the nearest spot to the violation (near the bench in this case) if only 1 FT was being attempted.
That's the super-strict by-the-book call. It seems over-officious to me and I would likely not observe the player leaving during the FT attempt.
