MAX_FALLDISTANCECOUNT is 60 for most known versions of DOS Lemmings and its variants; 63 for CustLemm and a version of Lemmings that came with Mark Tsai's solution book.
Note that the exact behavior also depends on the skills' exact implementations. DOS L1 had a couple glitches with respect to the max fall distance. Miners coming out of a vertical wall might splat whereas walkers falling from the same tunnel may survive.
Don't know all the values or physics from Lemmings 2. There are fallers, tumblers, divers, ..., which may need separate treatment.
L2 fallers walk after falling up to 67 pixels, stun after falling 68 to 102 pixels, splat after falling 103 pixels.
-- Simon