Recover Windows 7 license key from formatted drive

Since you have not overwritten your original drive, the odds are (slightly) in your favour.

You need to first recover the deleted partition, use a tool like TestDisk, you'll probably be best to use a copy from one of the variaous LiveCD's listed on their site. Be absolutely sure you read and fully understand the documentation before you attempt recovery - if this step does not work, your data will be lost permanently.

Once you have recovered the partition, you can then proceed to use a tool such as Magical Jelly Bean Key Finder to open the registry on your recovered drive and scan for your product keys. I have successfully used this tool to recover keys from registry files stored on alternate hard disks before and can confirm that this works well.

If you manage to recover the partition successfully, your chances of success in recovering your keys are pretty much 100%. If TestDisk (or whatever alternate tool you choose to use) fails to recover your drive then your key is lost.