After some further tests, we can safely close that one. The downtime was much shorter as originally anticipated and we were able to keep SSH up. Git repos should not be empty and continue to work as before, it will also not be required to set the fortrabbit master origin again.
Thanks for understanding and your patience.
All should be good by now. We are still monitoring the situation.
After a short downtime SSH & SFTP is now working again for Universal Apps. So only "Git deployment" and "SSH remote execution (only Pro Apps)" is not working until the expected end of the maintenance window, which is still a couple of hours to go.
Scheduled maintenance is currently in progress. We will provide updates as necessary.
Deploy server in US region will go under emergency maintenance, all deployments will be effected in US only, SSH will work normally.