I just want to find a secure and decentralized alternative to bitcoin
Which blockchain could become just as decentralized as Bitcoin?
Where could I store my assets in an emergency if there are no more bitcoins?
But why? You won't be able to find anything similar to Bitcoin. No shitcoin can compare to King Daddy. All other cryptocurrencies were created to imitate Bitcoin and/or make their creators rich eventually. So it's impossible to find a secure alternative, it's only a matter of time when the rug will be pulled.
Besides the scenario that he brings forward makes no sense at all, if for some reason bitcoin were to disappear then there will be no coin in which you will be able to keep your wealth safe, as I am sure that in that case all altcoins will disappear as well as most of them are basically just copies of bitcoin with a tweak or two, while the few that are original developments based on the bitcoin technology will still disappear due to the lack of confidence that investors will have at the time.