If ALL you did on the external drive was delete the partition, and IF the partition was formatted in NTFS or FAT32, then Active Partition Recovery can restore it. The free download will show you what it "sees", but you have to buy a license to actually do the recovery. [
http://www.partition-recovery.com/ ]
Note: You'll need a Windows PC to do the recovery on ==> you install Active on that PC; then attach the external drive to it.