Sustainability or the existence of crypto so far will not make it back to zero, but we do not know what technology will be in the future because as we know crypto is still difficult to be accepted by many people from various circles. So whatever will happen in the future I think everything is still uncertain, but if we only look at the history so far indeed, crypto will definitely be able to survive and have its own value and will not easily return to zero.
That's certainly true, mate. We do not know with certainty if another technology that's better than Blockchain, makes crypto go all the way to zero. As people always say, "nothing lasts forever". Bitcoin may have been successful since launch, but its future is highly unpredictable. Anything could happen from a full government crackdown into centralized exchanges to a 51% attack on the BTC blockchain. As long as crypto sees the approval of mainstream governments, while people continue to use it more thoroughly for daily payments, nothing should go wrong.
Nonetheless, haters or naysayers of crypto will say that crypto will go to zero in terms of price. I've seen this many times, yet crypto is still valuable and admired by people around the world. Blockchain technology has improved over the years, thanks to developers' efforts on the industry. With just 11 years of Bitcoin's inception, crypto has grown into a "force to reckon with" for people to recognize it as an alternative to existing Fiat. It'll hard for Bitcoin or any other prominent cryptocurrency to go to zero anytime soon since they're too big to fail. Small cryptocurrencies with no active development or real use cases for the mainstream world, will fail in the long run. As long as you invest wisely into battle-tested cryptocurrencies which provide usability above all else, your investment will last for a very long time. Just my thoughts