1. We’ll all die in the end. You can’t cheat the grim reaper.
2. Their grandmother was a very superstitious person and relied heavily on her intuition. She was convinced that she was about to die because she felt the grim reaper breathing down her neck.

The expression originates from the literary depiction of death as a hooded grim figure carrying a scythe (a farm tool made with a long, curved blade attached at an angle to a long handle). He uses the scythe to ‘reap’ people.