Though it's not likely gonna ever happen, but if this would really happen then I would sell all of my bitcoin, because I don't think it would stay in $1M for a long time. I'm sure when this happen people will also sell their bitcoin and that makes bitcoin price drop hard.
Yeah it never gonna happen. And even if it does, it would not survive the selling pressure. The only exception is if you vanish the Fiat and there is no option left except Bitcoins