It is being maintained and still actively used. The largest user, afaik, is Chia Network (
https://www.chia.net) and they rely on that for the bulk of their internal and external community comms. If Zoom decides not to host the servers anymore I predict they will likely try to acquire it from Zoom or re-implement the server portion.
There is probably a profitable business to be built to implement an opensource version of the Keybase server that is backwards compatible with the client and then start charging enterprises a reasonable price for data storage and communications to host it in the cloud. Zoom is sitting on a potential gold mine and they are just letting it languish.