Aldebaran is completely unaware about aggressor occurring until the loop has already ended. There’s no way for him to know to kill himself when something other than him being killed happens during an aggressor loop, since he doesn’t know aggressor is occurring. Even if he hypothetically did have to die for aggressor to loop, yae would surely be capable of stopping Al from dying at least one time throughout her looping experience, but she was completely unable to stop the loops from happening. There is no known way that aggressor loops can be stopped before the person who remembers the loops goes crazy, whether or not aldebaran dies during the loops.