Well, even though that is unlikely to happen now I will go through what would lead to that occurrence and what would happen if it happened now as a prediction. To begin with bitcoin would inevitably die where bitcoin would become truly useless and that nobody ever wants it; since it fails at its main purpose of providing a safe alternative to the modern currency and banks. This is because it has got exploited to gain money as it is unstable evident by its extreme change in market value which makes it unable to be used as an alternative currency, it would just make sellers of products using bitcoin not trust having this currency and seek changing it at the nearest opportunity.
Moreover, provided that there is a sudden decrease in the bitcoin value rendering it useless (0) it would mark the end of other crypto-currency as most crypto-currencies have their market value reliant on that of bitcoin and if it suddenly crashed most owners and investors would sell all of what they are holding out of panic and as no one would be buying it would decrease the crypto-currency market to a halt.
Nevertheless this is completely speculation I just have some information on crypto-currency and how they operate and also some minute information about marketing. thus i would love to see what the experts would say upon that question