Time of death from IBD varies from snake to snake, species to species. I had two long term captive boas come down with IBD. They were in a room with several pythons species - including a ball.
They were also in a rack with 10 pythons - none of which were infected. These boas were asymptomatic for over five years. The two boas who were diagnosed with it via esophageal biopsies had been mated several times over the years.
So in my very limited experience, it doesn't spread that easy. It takes a definite vector. On the other hand, an RI or other virus can be spread easily through the air.
I had a friend go through an OPMV outbreak and all of his affected snakes went very quickly with amazing amounts of mucous coming out of their mouths in the very final stage.
It could have also been an RI. There are several highly resistant strains out there. That's why it's so important to not administer antibiotics until a culture has been performed.