We're still in a hype phase, so anything can be expected in the following months. I'd say that the "De-Fi" space needs more time to mature before it can be considered a "replacement" of traditional banking. Even if it improves, it may not be able to replace banks in the future, as they dominate the world's economy. "De-Fi" will become widely used by the "unbanked" serving its particular use cases in the mainstream world. There's still a lot of room for growth, so I'd expect "De-Fi" to become robust in the long term.

I believe that once the hype cycle is over, this emerging industry will be put to the test. Only projects with active development, innovation, and real use cases for the mainstream world will survive in the long run. For what I know, nothing is perfect. There are many flaws adherent to smart contracts providing "De-Fi" services to everyday users. Banks on the other hand, are much more secure and reliable, leading people to trust them more than anything else. Besides, "De-Fi" is becoming practically useless with the extremely high fees on the Ethereum blockchain. Last time I've checked, I needed to pay $126 (USD) in fees just to withdraw my tokens from a "De-Fi" protocol known as "Instadapp". This is insane, as it's unpractical for the average person like me. Unless ETH upgrades to PoS and becomes more scalable, "De-Fi" adoption will be limited. While there are other scalable blockchain networks like TRON and EOS, they lack an ample ecosystem of dApps.

All in all, no one knows what will happen in the future. "De-Fi" could either survive or fade into oblivion in the long run. It's extremely risky right now, so I'd advice to proceed with caution. We should give it some time, for the space to mature. Only then, we can determine if "De-Fi" will pose to be a threat to banks' existence (which I doubt it) or not. Just my thoughts