A lot of "real" currencies – backed by governments with guns – have disappeared in the past, simply because people stopped believing in them.

Every currency ever created eventually disappeared. Nothing particularly special about them. The only reason people even bothered using them at all was due to government mandate: businesses are required to accept the local currency and taxes can only be paid using it.

Cryptocurrencies exist in a digital and decentralized world. They will outlast governments.

it's not like currencies haven't died before due to international boycott. And even internally there is a breaking point at which a sovereign that loses the confidence of its people is helpless.

We had other global reserve currencies before USD and they have all lost their reserve status, it can and will happen to USD too, as other countries become more powerful.

To be fair i trust a decentralized monster where millions of people have millions of their money in more than most governments.