If I'm understanding you correctly (sorry, I'm new at this) It sounds like you are describing an accident that either didn't actually happen, or was minor compared to what could have happened. I would call this a "near miss" or "close call"
Explanation:
For example: I had a near miss today when a dog ran out in front of me.
Or: He had a close call when his foot almost slipped over the edge of the cliff.
