In most jurisdictions this project wouldn’t have any problem, when it’s a “clean room” implementation - meaning they figured out by themselves how the server works.
Several jurisdictions even allow reverse engineering and such to ensure compatibility / supporting an product that hasn’t any official support anymore.
Others simply don’t care.
It’s all in the details, but they might not get sued that easily.
In most jurisdictions this project wouldn’t have any problem, when it’s a “clean room” implementation - meaning they figured out by themselves how the server works.
Several jurisdictions even allow reverse engineering and such to ensure compatibility / supporting an product that hasn’t any official support anymore.
Others simply don’t care.
It’s all in the details, but they might not get sued that easily.