This is an interesting part of the story of aviation. The long term lesson is that perhaps our non-destructive testing procedures aren't all they could be- so we need to learn how to examine things differently without breaking them apart ('we destroyed it in the inspection, but it was OK...).
I would imagine there are also other rotor blades out there that have been struck by lightning and inspected and have put in many hours of useful service afterwards.
This particular blade appears to have had a manufacturing defect that made the problem worse, and that was undetected in manufacture or the subsequent post-lightning strike inspection as well.
I'm reminded of the story of the Canadian F-18 that was overstressed to 11.2 G (ground static testing had only ever been done to 10.5G) - every non-destructive test known was done on the machine, and no fault found, so it was put back in service. Flew quite nicely for several years, so I understand.