Minimum safe altitude is that altitude necessary to ensure being able
to glide to a safe landing in the event of a power failure.

FAR 91.119 does not define minimum safe altitude based on the safe
landing of the aircraft itself in the event of power failure. It's
based on whether such a landing will result in undue hazard to the
persons or the property on the surface. Otherwise you will never be
legal flying below 500AGL over the open water.

U.S FAR 91.119 still carries the grand tradition that as part 91
flyers, you're allowed to do certain risky things, as long as you're
only endangering yourself. That's a great tradition that makes this
country great, folks.