If the slide thumb safety is engaged (angled down) the firing pin is captured and is drop safe. When I carried S&W 1,2, 3rd gen semi autos I carried them safety off, normally in a duty holster with hammer/thumb safety strap.
The model 59 has a magazine safety to where the pistol is not supposed to fire with the magazine removed. If pressure is applied to the trigger when the magazine is ejected the pistol will still fire one round as long as pressure is not removed from the trigger. If pressure on the trigger is released after the magazine is not locked in the well the magazine safety will be activated and the pistol will not fire without the magazine.
This situation can arise if there is a struggle for the weapon (model 59). Part of weapons retention training when I was carrying 39/59 was to push the magazine release when struggling to maintain control of the weapon. If the magazine falls on the ground and the Officer regains control of the weapon he probably has a spare magazine where the offender probably doesn’t.
