I don't know about the MD500 but any helicopter with a rotor speed governing system will quite happily run with both engines running with the rotor blades removed.
Quite difficult to believe in some cases. I remember running a 332 in storage without blades and the engineer beside me was having kittens as I went through the normal start with the first engine and then straight into the second.
It was sitting quite happily at about 270 Rrpm with both engines well above Idle.