Are there any alternative SSH servers other than SSHD?
One that is not SSH based? Ideally one that can be installed from offical Debian repository, that listens on a port other than port 22. (To avoid conflicts with ssh from the beginning.)
Must be secure as ssh (authentication, encryption).
Emergency login if SSHD does not come up after reboot.
No non-SSH based out of band server management for a server available.
Mosh looks nice, but it is also using ssh in background, so of no help for this use case.