Disk utility killed my external drive
Running Diskutil in command line mode is pretty much the same as running it in the GUI and that is the right way to go: select the disk and click on repair. Or do it the way "perhapsmaybeharry" indicated. Either should work.

If that fails you may need to try a dedicated disk repair program (I use Diskwarrior but there are others that work well too).

Likely a bad sector cropped up at the wrong place at the wrong time that the drive firmware could not fix. It is unlikely that Disk Utility did anything. And another disk repair utility may be able to fix this.

If it can't you may have to send it off to a data recovery company, but that is expensive and DiskWarrior (or others) is likely to fix it.