I guess crypto will never go to zero especially the useful ones because if crypto will go to zero I think it will never been made in the first place, it is implemented because of the use of blockchain technology so I think the only crypto that will go to zero are shitcoins which are no use at all.
Don't be guaranteed of anything in the crazy world of cryptocurrency. Because here anything can happen. During 2012-13, no one would have thought that Mt Gox, which had more than 50% market share at that time would sink without a trace. But it happened in 2014. Another example is with Cardano. It gained so much hype in 2017, but went down by more than 99% a year later.