It's also extremely naive to assume it will be easy to transfer a massive decentralized project to a post-quantum algorithm. Maybe new cryptos will be invented, but Bitcoin will not "retain value".
Things that will retain value if the entire internet is broken due to rapid deployment of quantum computers will be:
- Real estate
- Physical assets (gold, silver, etc)
- Physical stock certificates (printed on actual paper)
- Paper money
Since internet, cards, finance may just stop functioning one day as quantum computers break all encryption.
Feel free to prove me wrong.