Suffer a severe reversal, as in If they can't raise the money in time, they'll buy it. [Slang; mid-1900s]
Be killed; die. For example, By the time we could get to the hospital, he had bought it. Originating during World War I as military slang, this term later was extended to peacetime forms of death. A later slang equivalent is buy the farm, dating from about 1950. For example, He'll soon buy the farm riding that motorcycle. According to J.E. Lighter, it alludes to training flights crashing in a farmer's field, causing the farmer to sue the government for damages sufficient to pay off the farm's mortgage. Since the pilot usually died in such a crash, he in effect bought the farm with his life.
Believe it; see buy something.