Out of bounds.

[SamIAm]

Casebook 7.1.1 (B) hinges part of the legal/illegal issue to the player having control of the ball or not before going OOB. It indicates it is legal because the player did not leave the court voluntarily and the player did not have control of the ball before leaving the court. In the posted sitch the player dribble one or more times, left the playing court, then returned to continue dribbling the ball.

I see nothing in the post that fits the definition of an interrupted dribble.

I see no reason not to call an OOB violation. The only difference to the (I can't locate the rule) violation of stepping out of bounds while dribbling is the direct angle in this sitch versus the player dribbling along the sideline and stepping OOB while not in contact with the ball.