Private servers are a thing for lots of big games. When the official servers shutdown or go bad, they tend to turn to emulation
Private servers don’t really happen much or at all anymore, “here’s a .exe you can run” idea doesn’t scale on modern online infrastructure well
Emulation is typically a very difficult thing to do, often requiring cracking the original game to get it to work with non official servers and also mapping and building out all the online subsystems. It’s rare.