Some of your statements here seem like tautologies. You're saying the actual world must have the potential to continue to exist or to cease existing. I don't know what kind of necessity that's supposed to be (natural, metaphysical, or logical).

But okay, so a changing universe is a reality and something's keeping the universe going. As to the nature of that change, we can answer as physicists, philosophers (metaphysicians), or theologians. So sure, there are possible answers to these big questions.

But you seem very confident in your answers, and I'm trying to see what the basis of that confidence is. Are you relying on these kinds of deductive, analytical arguments that turn on the analysis of certain concepts? The problem with those a priori arguments is that they might reduce to semantic choices about how we prefer to define our key terms.