On the subject of everything being destroyed by the black hole: would it even matter? The timeline inside a universe frog does not run parallel to the outside of the same frog; the creation of the green sun and the destruction of Earth's original universe didn't stop Roxy et al. from existing even though it was in the same frog. The lifespan of Earth C's universe will reach its natural end independently of whatever destroys it, if anything. Besides, doesn't Earth C become Caliborn's planet?

Earth C is Caliborn’s Planet, yes, which in fact does imply the Universe C has at least a few billion years ahead of it peacefully. That doesn’t mean the end would NOT come eventually, and given the fact Paradox Space is being shattered, there’s a question whether other new Universes could be also spawned after all of this.