This is true: if Bitcoin has still any usability, 21M of bitcoins are a too small number to keep the value to $1. There are too many people that would buy huge quantities... therefore the only reason that would make its value fall so low is that it doesn't work (hackable? unsafe? Transaction takes too long to be confirmed because blocks are still only 1M? And so on..). At this point it loses all the value so most likely it's 0.