Well, the code is still there, and nothing should be broken in it (give or take the outdated and potentially vulnerable dependencies).
I no longer believe that abusing Discourse’s SSO APIs for logging in with Telegram is the right way to go, though (thus the repo is archived).
Much better solution would be a plugin adding a Telegram button to the supported auth options on the login popup/screen — but this would require quite a different approach, and I’m not aware of anyone trying to do this (even if it is 100% possible, and I remember seeing other plugins with similar functionality using other login networks somewhere out there)