Depends on how they licensed various libraries used in the server binaries. Some of them might not allow redistribution of the final product, only provision of digital services.
That's a non-issue, those providers would have to relax their licenses, since releasing binaries after EOL would become expected of all.
Alternatively, as SKG suggested, Riot could post the spec needed for a server to communicate with the game, and someone could just write a server for it.
All hundred different microservices? And I'm sure you also want docs for how to run them all together too?