It's actually possible to save 49/50 by using the digger on the left so that only the bomber dies. (The original game has 50 lemmings on this level.)
But this depends on the way steel was handled in the original game. Destructive skills would consult the steel map to decide whether to stop, or, in the case of bombers, whether they could remove terrain or not -- but any stroke of destruction that did go ahead would remove all terrain, including steel, within its destruction mask.
That behaviour is undesirable for custom levels because it makes it possible to create paths through areas that the level designer intended to be impassible, so NL instead makes each stroke of destruction remove normal terrain without removing steel. This makes it impossible to take any right-side solution on Compression Method 1.