[He's so set on being alive because it's impossible for him. While Zeno is absolutely sure that Kaya came from her death, he can't say for sure that she didn't die as far as her timeline is concerned.
Even so, Zeno has no explanation as to why she's alive here now except that it can't possibly heaven.]
I don't know the answers to that but I'm sure that Kaya isn't dead and this isn't heaven. But it's a good place to be if Kaya is feeling better.
[That's not entirely true. They are in prison so not everything can be nice but it has given him a gift that he never thought he'd get.]