The actress portraying Izzy, Zyra Gorecki, does in fact have a prosthetic lower leg. It is not CGI.
The light that the survivors fall through at the bottom of the sinkhole that now appears in their new sky is the same "rift in time and space" that follows Amy Pond throughout her arc on Doctor Who (2006).
Before the end credits, there are glimpses of what is in future episode, and they show written "Where Are They?" and then Where changes to When, giving "When Are They?" At first it looks a mistake in sentence construction, but then it introduces angle of a time displacement movie, meaning they are still in LA, USA, but are in some other time-span. This increases curiosity.