This assumes that you use summon greater demon (Xanathar’s Guide to Everything, p. 166), and command it to attack your enemies. This summoned Balgura succeeds in killing all enemies you ordered it to, but during this time you were drawn away from the demon, and haven’t been able to issue it a new verbal command. Keep in mind, it hasn’t succeeded in breaking the spell via it’s CHA saves.
Would a Demon be able to act on it’s own accord if it hasn’t been given any new commands, and has no creatures to attack that "attacked it during the last turn."?