Severus took a deep breath and sighed softly as he exhaled. "I don't know," he answered -- mostly honestly, at least, even if he could explain a bit further. But he waited until he was on the other side of the gate before continuing.
"I've heard that there are doppelgängers to replace us when we're brought here, and I've had former students of mind confirm that I never went missing, even though I am here." He sighed again and shrugged, before adding, "But I suppose it's possible."