I’ve heard both but the “if one of the bottles should happen to fall fall” version always sounded really awkward when “down” and “around” rhymed a bit better.
I only heard the “fall” version at a camp and that was just one year when a more Christian-leaning director decided that as we were all kids, the equally underage counselors should promote drinking alcohol, so they had to “fall” not be “passed around.”
I wish there were two options. My childhood memories are 99 bottles, but the verses I know are:
“(You) Take one down, Pass it around”
and
“If one of the/those bottles should happen to fall”
not the ones given in the OP. (I can’t quite make those versions scan to how I know the tune.) This is how I know it, sometimes with the “you” omitted.
We sang it on a car trip to Montana. My uncle bet us we couldn’t sing it backwards in the same amount of time. To the consternation of the other adults in the car, we proved him wrong.
99 bottles get passed around, and I learned the other one as:
*There are ten green bottles
a-standing on the wall.
There are ten green bottles
a-standing on the wall.
But if one green bottle
Should accidentally fall.
beat
There’ll be nine green bottles a-standing on the wall!*
We start with 99, and alternate between passing them 'round and
*
if one of those bottles should happen to fall
what a waste of alcohol!*
[resume count one lower]