As said we are not there to plice the skies - but if I saw you descending quickly I might ask if you are OK.
The issue of breaking low flying rules is not really ours. You should know the rules. If, however, we were phoned about an alleged breach then we are onbliged to give all the information to the authorities.
But the rules are for the protection of you, your aircraft and more imprtantly people on the ground. If the engine did go pop and you were below the 1500'/500' rules then you are in the pooh! If you were to hurt or cause a fatality I think that you would be up for manslaughter.