I may be wrong, but I don't think that Magificat would go back to the discard pile. I think once it enters play, it stays there, even though Ethan is negated.
While I agree that this is the way that it SHOULD be, the official ruling from the Elders has been that a card that has been played does not "stick"
unless it is CBN (or played with a 'play' ability, which is inherently CBI). If it is not CBN, then it can be returned to where it was previously if the ability that pulled it out is negated (draw, search, exchange, reveal, etc.).