well you could argue that there were only two (plus lain) witnesses of the headset being destroyed, and that Alice was hallucinating the whole Eiri-time. Alice after all is a rabbit hole kinda girl. i can't really advocate this theory any more because;
I always thought of lain as god (in some sense of pantheism). lain is matter, lain is energy, lain is chaos or rules of physics, lain is maths, lain is whatever anyone has ever pointed out as the source of all else, etc. it's unnecessary, and would make all fiction ever made tell about just a small aspect of lain, incl SEL. but hey, she a qt!