If you don't have it in mail in the form of an attached job log, you'd only be able to restore it if you have a copy of the bedb.bak file from before it was deleted.
Be aware that this might cause some issues, as you'd need to stop all your BE services + the SQL service; grab a copy of the Data and Catalogs folders (JUST in case things get messed up!); and then use the BEutility.exe utility. You'd right-click your server name, and choose the option to Dump database and reload from backup. This will reload the BEDB as it was at the time of the maintenance backup. You can then save the job log.
If you don't have a bedb.bak or SQL backup from a date before the job log was deleted, you can't recover it. You can catalog the tape and then see what's available on it.
So the daily backup of the BE database is done at night at 4am everyday. If you deleted job logs, you can recover the database from last night using BEUtility.exe on the program directory, and choosing Recover Database, Reload from Backup. You wil obviously lose all changes from 4am to now.
Before doing this stop the BE Services and make a backup copy of your DATA folder first! As warned above.