@OP, you are talking about digital assets replacing cryptocurrency. Have you ever thought of or researched on what digital assets are. Cryptocurency is an example of digital asset, since it is something that has value, with online presence, but does not have physical presence. There are also other forms of digital assets, so you need to be specific on which you think will replace cryptocurrency.
In my own opinion, we are yet to see an end o cryptocurrency. It has a great future ahead of it.
Cryptocurrency can be a digital asset only if it adheres to several procedures. Cryptocurrency itself is more of a speculative financial derivative that has a certain speculative value, similar to contracts for difference or options. Digital asset, on the other hand, implies the existence of a certain asset.