I don't think it will drop in a single day or even in a short period of time. Too little people own too big of a percentage, so even if all smaller owners would sell within a single day, most of the btc will still be locked unless the big players decide to sell.
Maybe people should even stop imagining things that would not likely happen but instead imagine that the chance of more people buying bitcoins is far more than everyone dropping their coins. What is the point trying to imagine a doomsday that obviously does not sound realistic and I wonder why a lot of people tend to derive pleasure in that, which is either they are just not understanding that as a market is growing, there will always be chances of more people coming in and as long as the market becomes usable, all these things being said by the OP cannot even come to reality.
If everyone sells bitcoin, its price will drop greatly. Since many coins are dependent on bitcoin, I think that a drop in bitcoin will cause the entire cryptocurrency market to fall. Bitcoin is not for everyone.
If everyone, but not everyone is dumb enough to be selling when the market is still very young and believe me there are so many people who are focusing on the long term than having to sell in the short term which is the main reason why they find it so easy when it comes to investing for the long term and holding for as long as they can, and at least, that has shown the number of big holders that are still holding as much as they can till date. As long as the markets have prospects, it would grow, become usable and demand and supply will obviously get balanced.
