Regarding the Emperor introduction sequence, I would think that as soon as we enter the Astral Prism that we would well... be in the Astral Prism, so defeating the Emperor then and there probably shouldn't be a Bad Ending trigger or at least a different one where we are trapped in the Astral Prism forever (unless we could side with the honor guard and they could break the Orphic rocks like Orpheus seems to imply).