If we talk about the worst case scenario then to me it will be the collapse of crypto market.

First of all it is almost impossible that bitcoin will hit zero or 1$ and why it is impossible to hit bitcoin zero because following must be happened. 

All the countries joins together to enforce the ban on bitcoin. 

All the countries start to crack the bitcoin holders. 

Bitcoin develop a bug that its developer unable to solve. 

If this scenario is developed then what will happened. 

Bitcoin holders will lose all their investment. 

Crypto currencies will lost their complete trust and as a result all the currencies will become to zero.