Nothing last forever, and the Fiat world will get a hard time in the future, when crypto slowly takes over.
BTC for now is doing good and in coming few years also should be doing great only. We do not know what might happen say after 10 years or so as the technology keep changing something better in coming years may come and due to which it can crash.
You can't know anything for sure but block chain technology is very promising and it can really solve some global financial problems. If you look at it that way then you won't doubt the crypto. It will endure no matter what because the idea is good.