What you can do to backup the server without admin panel access:
- rsync all websites to your machine (ubuntu or windows using Git or paid options)
- dump all dns zones
- backup multiple mysql databases:
mysqldump -u root -p --databases db_name1 db_name2 | gzip > full_backup.sql.gz
I always recommend users to purchase servers with snapshot management. If you had a snapshot before the upgrade you would just reverse it.