You can log in once and use your local firewall to block internet access to the game and it'll keep functioning forever.
The main reason for the account system bound to your purchase is that it makes it massively easier to moderate online game servers.
It also allows us to distribute binaries more freely such as the community contributed Linux AUR and Flatpak Packages.
> not everyone has the means to periodically authenticate
But I just wrote that you don't have to. If you set it up right, just one single time - forever.
> in 20 years your servers aren't going to stay up.
Should at any point the VS servers get intentionally shut down, you have my blessing to remove the login protection from the game - a skilled programmer can do this in 2 hours. Or build your own authentication server. The game is written in C# and intentionally left unobfuscated, so it can be decompiled back into C# with freely available tools within minutes.
That being said, each to his own. You are free to not buy the game ^_^
