I ran into this problem after updating the plastic client through its built-in update feature that downloads the client installer only.
For some reason that installer seems to have also decided to uninstall the server component without asking.
After manually downloading and running the full installer (incl. server component) the server is back up again with no config lost and the license problem is also solved.
I strongly suggest that you change the client installer to not remove the server component without asking. Ideally the update feature inside the client should download the appropriate installer, client or full, depending on what's already installed on the system.