What a bummer. We helped map the Kerrville floods for support of the state. Same day we mapped it, so did this WB-57 - only 35K feet above us. Such a historic and unique aircraft - I feel bad for the pilots onboard knowing it will likely total that aircraft even if it was a mechanical failure.
One of them was returned to service after 40 years in the boneyard in Arizona, back in 2011, I would expect they'll look at the other airframes there to see if they're suitable sources for a rebuild. Wouldn't be surprised if this is the end of this one though, it was already doing pretty well for a design that first flew in 1949 (the English Electric Canberra design that was then built by Martin)
That depends on a lot of factors. What is the damage, how much would it cost to repair, and is spending that much considered worthwhile by NASA or whoever owns it? (Or whoever buys it after this)
>> The pilot then maintains control of the vehicle
This seems to have been a training flight. Im sure the black box (if there was one) heard an excited "i have control" from the senior pilot once the grinding noise started.