Is there any backup for ssh configuration, to roll back on error?

Solution 1:

There is no need for a fallback configuration if you test your configuration properly, i.e.

Be connected to the system via SSH
Change the configuration of the SSH server.
Test the configuration using the -t or -T option of sshd.
Restart the sshd while still being connected. This will not close the current connection.
Try to create a second connection to the server. If this fails you still have the active first connection to reinstall and test the previous configuration.