Well, someone has to be buying all those btc at the other end. It might drop a lot but I find zero unlikely.

"Price drop to 0" literally means nobody's buying it, of course. If everybody (in the absolute) suddenly decided they didn't want to hold bitcoins, the price would indeed be 0, since there wouldn't be any buyers. (It might even be negative in some cases - you'd have to pay someone to take it from you.)