I recently had my '74 Ric 4000 slip out of its bridge-side strap and fall straight down.luckily it hit the cable end(and broke it) without any damage to the input jack or bass,but i now have straplocks on it. This was right at the beginning of a set,we hadn't started playing yet. I seldom take a backup,because that is the only mishap i've had in 30 some years....but check this out. Last week in the Bay area,Stanley Clarke did a couple of shows,and there was some problem with his Alembic,so he had to do an entire set on URB,because he only brought one EB! (This was a first hand report from a good buddy of mine,i found that to be really strange for a pro like SC!)
There is another well-known pro that only uses one bass.
Mr. Jeff Berlin reportedly owns one, yes just one, bass.