1. You cannot restore your CM using SQL backup only. You would BARS backup to restore the system once CM has been re-installed on the box. Since the backup contains failes, database backup and registry backup as well, only using SQL would not work.
2. The only supported way to restore if u have a failed upgrade would to go CM 4.1 and then do a BARS restore. Since a lot of files are replaced and the backup process does not take a backup of all the files needed. Therefore, you might have to re-install CM 4.1 (Depending on which stage the upgrade failed) and then do a restore