[GW150914]

That’s a question which may or may not be meaningful in the first place. In the classic formulation it’s a meaningless question, because time and space expanded from a singularity in the BB event, so there is no “before” just as there is nothing into which space expanded. The vacuum exists within the context of spacetime and the universe after all.

Maybe it was part of a cyclical series of events as you suggests, Big Bang followed by Crunch, and then Bang again. Maybe the String Theorists are eight and it’s cyclic and ekpyrotic, and our universe is just a burst of energy release by interacting Branes. Maybe none of that is right and some other model which better fits observations and predictions will turn out to be better.

One thing to keep in mind is just how tricky it can be to ask seemingly good and simple questions about these things. People come into this with a lot of assumptions and intuition that tends to fail at thes scales. Classic questions that don’t actually mean anything in the formalism are, “What is space expanding into? What came before the Big Bang?” There are other models which accommodate these questions such as eternal inflation in the context of a multiverse, but not in the formalism.