There's no way to really know what the state of the drive or the data is until you look at it with a dedicated recovery tool.
If it was my drive, I would remove the drive from the USB external case, mount it in a machine as an internal drive, and run GetDataBack for NTFS.
GetDataBack might take forever to scan the drive, but it will usually recover data if anything on the drive is readable.
From the failure mode you describe (power surge), it's unlikely that the drive is damaged internally (platters/heads), except perhaps a certain small range of sectors that were overwritten during the surge. A far more likely scenario is that the logic board on the drive is fried. If that's the case, a swap of the logic board with one from an identical drive should at least allow GetDataBack to run and recover some data.
Of course, there's no guarantees, and anything you do to the drive will at a minimum void the warranty, and possibly make the data harder to eventually recover.