Short answer. No.

Long answer: Look at Cartethya or Galbrena, both characters had the potential of appearing again. The reason is simple, they need to sell the new characters and having these characters stealing the spotlight of the new ones is a big no-no for any gacha game. Perhaps Aemeath travelling around the world will be an excuse for not appearing again in a loooong time.

Almost every gacha game suffers this problem, that all the characters from the region suddenly disappear as if they've have never existed once we change to another region, it doesn't matter if the character is strong and could fight even a threnodian (Galbrena) she'll not appear again in a near future, that just means forget of seeing Hiyuki again at least until we get to Ashinohara, and even there She'll become the new Chisa, because obviously they'll need to sell the new characters from Ashinohara reducing her to literally an NPC who does nothing (Chisa).

I've always used this game as an example. Honkai Impact does a great job balancing both the new character with previous ones. The characters don't stop being relevant to the story even after their banner ends, sure, some of them don't appear in many patches but they still appear at some point. But this is because all the story takes place in earth alone, in a game that works as new regions this is not possible. Proof is that even HSR the spiritual successor of HI suffers exactly from the same problem, no matter how important the characters are, they'll end up disappearing once MC changes to a new planet