[William A. Baurle]

After searching around, and being bombarded with crap from the Net, I think this link might be sorta kinda helpful?

https://www.quora.com/What-would-hap...yed-in-mid-air

Bits:

However, technology has progressed to the point where the same warhead of high yield could be compressed into smaller warheads. Coupled with the ability to have multiple independently targetable reentry vehicles (MIRV), you have multiple times the strength of the first nuclear bombs.

But back to the question, what happens when a nuclear bomb is intercepted? Thankfully, the casing that holds the concoction necessary for a nuclear explosion is extremely tough. However, they obviously can’t test a live version. We have past incidents that showed what happened to the older models.

During the 1966 Palomares B-52 crash, or the Palomares incident, a B-52G bomber broke upon upon collision with another plane and dropped its load of 4 hydrogen bombs! Fortunately, three were found on land quickly but the non-nuclear explosives in two of the weapons had detonated upon impact with the ground. It did not cause a chain reaction but only caused a leakage of the “dirty bomb ingredients”, resulting in the contamination of a 2-square-kilometer (490-acre) (0.78 square mile) area by plutonium. The fourth, which fell into the Mediterranean Sea, was recovered intact after a 2½-month-long search.

The whole reason why creating a nuke is so tough is because precision is what matters: multiple explosive lenses have to be perfectly placed and go off at the same time. Plutonium or uranium is not like conventional explosives- a fire or a fall will not set them off.

What would most likely happen therefore is either a blanket of radioactive materials falling to Earth or multiple warheads that fall to the ground which immediately deserve a search and recover operation!