tdracer
the FAA has made Boeing show that the rest of the aircraft can readily handle the blade out vibrations for an extended ETOPS diversion - it wasn't trivial.
One story was that after a blade out event on a 747, the aircraft vibrations were so severe the crew had difficulty reading the flight deck gauges (one variation of the story - perhaps antidotal - was that there was a Boeing exec on the flight - after the flight he promptly asked engineering to go make sure the aircraft could handle that level of vibration..)
The FAA also included all other plane manufacturers as well in the assessment. Tis true some interesting windmill events did occur but they were all associated with the loss of the engine front shaft support and did not otherwise degrade other critical structures or the ability to fly the aircraft.. Nevertheless the loads developed were well within the design loads for manuever and gust loading in the aircraft certification base.
The worst part of it was that the passengers were not happy as the aircraft went through a critical windmill speed range while landing.
As for reading the flight deck instrumentation we confirmed that the crews could fly the aircraft with no problem. We got one famous chap to sit on a laboratory shake table and cranked it up to the expected frequency and amplitude for a time and he had no complaints and slept for days afterwards.