yeah, they pretty much said that when Sakurai used the card, since Ryoutaro wasn't Den-O yet (?), the memory of the baby disappeared, so when Ryoutaro's memory was used to recreate the present, the baby no longer existed since he didn't remember a baby
the question mark is cause they never really explained how come Ryoutaro's memory was effected by the Zeronos cards, when it isn't when Yuuto uses them, i'm guessing it's cause he wasn't Den-O yet, but yeah, they never said
[spoiler]which in turn you can guess that, that destroyed the time in which Hana existed since she no longer existed technically, but because she is a singularity point, she wasn't erased and somehow ended up on the DenLiner[/spoiler]