Having part of the star form accretion disc and then slowly radiate the energy is entirely different from the star converting significant part of its mass into

Having part of the star form accretion disc and then slowly radiate the energy is entirely different from the star converting significant part of its mass into energy and radiating it in couple of hours. Also jets are highly directional and you have good chance to be away from the cone. I am not a physicist but I suspect that extremely active star turning into black hole might be much less luminous than the star itself. Accretion disks can be very luminous but this is typically for very large holes in the centers of galaxies. Because we observe these huge stars only because they are so highly active, the act of converting it to much less luminous system might be undistinguishable from the star disappearing.