after 2025 BTC , ETH and so on will be worth real 0.
I do not know - what about USA, CHINA and so on. I'm talking only about EUROPE.
or perhaps the European Union will fall apart.
In case of a ban within the EU the BTC price would be much higher within the EU than outside of it. Black market prices always come at a premium.
Either way I don't think CBDCs will become much of a thing within the foreseeable future. Sure, governments will dabble in it and some people will use it but I don't think it will replace cash any time soon. Even for societies that are already cashless the incentives to switch to CBDCs seem to be rather limited.