I'd need to check how long the validation lasts, since it may be well be like emulated PS1 games from the PSN ("PSOne Classics") and Steam's offline mode, both that take a few years to reset, but neither permanent.

But about people complaining, they usually do so only for problems that are obvious to them. And the obvious is usually immediate.

And if it takes a few months/years to expire, I'd say it is not ethical, but pretty vile, as then people will not notice the problem at first, and when they do, they may no longer access their contents.

And considering people that forgot to upgrade their original Mojang accounts, or didn't have access to the needed tools while the change to Microsoft accounts happened, there is a precedent for Minecraft validation methods to not become available any longer.

Also, from my experience with Windows Vista, where even though I have an actually original key for it, if I try to install Vista nowadays and try to connect it to the internet, it will lock the whole system from my access on the next start-up, I'd imagine because it can't reach the validation servers. So I've seen first hand how Microsoft's preservation goes over several years. And since Minecraft may also be used online due to multiplayer, checks may still happen, and being nowadays also a Microsoft product, it may suffer from the same vices of origin.