Because I'm that kind of a person, I would accept the numerical title only if using Roman numerals...
More serioulsy, although I appreciate their sobriety, the more I think about this one and the
Godfather-style one, the more they feel irrelevant to me. Sure,
The Batman had somewhat of an open ending, but there's high chances that things like the flood will actually be addressed in the Pinguin spin-off rather than the sequel. And so, I don't think that new trilogy, in itself, should really be seen as one big story divided into three parts.
I don't know if that makes sense for everybody, I admit that there's a certain psychological rigidity on my part here...
Otherwise, between the last two, I think "Finish the sentence" is still a fresh way to name a sequel opposed to the much more formulaic subtitle. So, this is getting my vote.
But really, in the end what matters most to me is that the title really reflects the atmosphere of the film. And as long as it has a nice ring to it and isn't too
cheesy, I'll go with it.