Mosh with port forwarding (like SSH)
I found an open issue for this exact feature at Mosh's GitHub. And an open bounty at bountysource currently at $616.
So it looks like it's not possible yet.
As a workaround for my SSH disconnect issue I added the following lines to my server's
ClientAliveInterval 60 # send null packet every x seconds to clients
ClientAliveCountMax 720 # time them out after doing so y times
Followed by a restart of the SSH daemon and a re-login via SSH.
sudo /etc/init.d/ssh restart
sudo service ssh restart
sudo systemctl restart ssh
This of course doesn't help with situations like changing cell towers on mobile connections like mosh does.