It's the last sentence of an article in The Economist.
Some of the powerful elders might have faded from the scene. Mr Xi and Li Keqiang might then have a freer hand to promote their own people, and perhaps more daring ones. If, that is, they manage to keep control until then.
I know the whole sentence means "it is possible only if they manage to keep control" or "it's impossible unless they manage to keep control". But I don't understand how it functions.
Question 1: What does "that" refer? Or is it just an empty word refering to nothing?
And I also have a question about the reference of "it" in "It is not until 3am that they returned home." I think "it" refers to the fact that "they returned home", and the sentence can be restructured as "the fact that they returned home is not true until 3am." Though it sounds wierd, but it helped me to understand how "it" functions. But some people tell me "it" doesn't refer to anything in that sentence, and I shouldn't comprehend it that way.
Question 2: Am I really wrong in the understanding of "it" in that sentence? If so, how do you think I should understand it?
So everybody thinks that is is short for that is to say? But I really think it would be anything but that is to say. Before I asked this question I tried to comprehend it that way, and here came an absolute logical error: since that is to say usually connect two sentences expressing a similar meaning, the two sentences should be in the same type of pattern. That is to say, if the previous sentence is a statement, then the following one should be a statement as well, despite all the clause and parenthesis. But the sentence I quoted is just a conditional clause, and its previous sentence (sorry for not having quoted it earlier) is a statement.