I don't think the floor price of crypto is zero. It may be low but there will always be some use for it, if not for criminals or people living under authoritarian regimes to avoid the law.
Increase Bitcoin's fungibility with Schnorr signatures or Litecoin's with Mimble Wimble (in the works right now) and you could say that both of them combined with second-tier solutions to help them scale are the best form of money ever invented by humanity.
Floor price is always zero. It isn't likely though.
In practice it won't be because of the small amount of baseline demand for the purposes I mentioned.
Yep. the chain would have to halt and @gtg won't let that happen ;D