lol! I'll choose B - Died of fright. Several years ago we were on
vacation and my brother-in-law was checking in on the cats.  I called in
the evening to see how everyone was doing.  My sister-in-law said the
cats were fine but that BIL had walked into the kitchen and found a
squirrel that was in the final spasms of death.  There weren't any signs
of the cats actually injuring the squirrel although she did say there
were signs of a chase through the house (placemats on the floor instead
of the table, table runners askew).  I had the same choices you did and
determined the squirrel must have died from fright combined with over
exertion.

Julie

We'll never know. This reminds me of when Frank caught his first vole
(he was ten years old at the time). My sister, who hadn't been very
impressed with his hunting skills thus far, claimed that the vole had
probably committed suicide by throwing itself in front of Frank and
saying "Take me!"

I'm going with the Mothership theory.