There are three categories of live service games for which fans have reverse engineered a server:

1) The server doesn’t do much other than connect the players, and most of the logic is either client-side or trivial.

2) The server contains a fair bit of game content (such as drop and spawn rates, maybe even NPC dialogue) and the community has done extensive packet captures while the server was online.

3) The server binaries were leaked at some point, and everyone agrees to keep it a secret and pretend they’re doing a clean-room reimplementation from packet captures. They are, but against the leaked server, not the production server.

Having worked on a few of these projects, you’d be surprised at how many of the successful ones are actually #3.

This is problematic because we can’t rely on data breaches for game preservation.