IIRC if fstab is empty the system doesn't know what filesystems there are. If this happens the system will boot to single user mode. It'll ask which shell you want to run. The root filesystem / will always be mounted read-only. After a filesystem check a mount -u / will remount root read/write.

Usually /etc is on the root filesystem, so try to find out where it filled up.. And AFAIK if the filesystem fills up it doesn't destroy existing files. So I'm not sure why fstab is empty.. Maybe some admin nuked it? Perhaps it had a crash and that corrupted fstab?

DO NOT clean out /etc! There are lots of config files/startup scripts in there that are needed to properly boot.