There is no way to roll back a factory reset. There are, however, ways to recover data from the internal drive.
As always, if your are dealing with a potentially catastrophic loss scenario make a copy of the current state. The time-tested way is to clone the state by using dd via the adb (Android Debug Bridge) tool from the Android SDK. Guymager may be an alternative but I haven't used it for this purpose yet.
After creating a clone you can attach the phone to a PC and try your luck with Testdisk or the less powerful but easier to use Recuva (MS Windows only). If this is not working out, bring in the big guns.
Get a copy of Paladin (it includes Autopsy/Sleuth-Kit, a powerful forensics tool) and start digging. Be warned, this can take a long time.