Sheesh — the shear thought of it gives me the heebee jeebees!
You can run the free trial of Stellar Phoenix Mac Data Recovery on your unmounted WD external hard drive.
they will diagnose you for free, repairs may cost you if you are out of warranty.
One of the old Mac OS X utilities, Disk Utility, has received a makeover in mac OS Sierra.
And repairs can take a long time (overnight is not unheard of) so unrecoverably damaged disks often initially diagnose similar to what you are seeing.
Failing other disk utilities or other Macs your best bet might be a visit to an Apple Genius.