Well, if it's gonna be a usual VG to Kanan-thing, I think they might find a replacement. Whether Tact married Mifeulle or not, I think the Moon and Rune angel-tai wat Milfeulle to live a happy life without any gatekeeping and such.
l think that they will find a sutible replacment in the very last game. I don't know who, but hopefully it's not one of the Rune Angel -tai.
Natsume, judging by her outfit, looks like some kind of princess or someone VERY important to NEUE, so she could be important to the plot. who knows?
About the middle comment, I have no clue. xD This is what I get for being too young and having stict parents!
Maybe they'll use it? I dunno what the angel phaser is like, but if it's like the Chrono Break Canon, which
was used countless of times in the first trilogy, then it might be used in the 2nd maybe even third GA II games.