I went everywhere before DD was born so I could see being in a theatre. I personally wouldn't have asked for a refund, I just wouldn't be bothered by the $20 loss. If my water broke I would have or DH would have offered to clean it up. For most people, water breaking doesn't not mean going to the hospital immediately. My water broke at home and I stayed home for about 5-6 hours after until contractions were stronger. I was able to shower, etc. as well.
That said, I worked at a theatre for years, I would have given the refund just for business image. It is bad for business if customers have negative stories.