I have some ideas:

What about the remaining Grimoire Heart members?

- Hades: Killed.

- Bluenote: Member of Orochi's Fin.

- Ultear: In hiding after her sacrifice.

- Rustyrose: Seeking to revive his former DG.

- Meredy: Redeemed.

- Azuma: Dead and turned into a tree.

- Kain Hikaru: Unknown.

- Zoldeo: Died.

- Zancrow: Killed.

- Yomazu & Kawazu: Unknown.

With Yomazu & Kawazu as too minor as characters, I think Kain Hikaru became a member of them. This would be a good plot twist and the final reveal, where the major members of Grimoire Heart went after the BA's disbanding.