This would only happen if most of the countries start to ban Bitcoins, but this would not happen.
There are multiple factors which can affect the price drop and price gain and no one can predict what would be the price after one year. There is no algorithm or method to predict future price of Bitcoin.
They can't. They just can't ban all crypto in the world. They want to regulate it but it doomed to fail. US is smart only to tax is. Dubai, singapore, Estonia are even smarter to join in the revolution of crypto. Let see. In the future we will see.