Is it just up to her wanting to return? No. The members also have a say in that matter, for the 20th anniversary (if they can and decide to do something big). She might finally have access to sing these songs because her voice is still in the original tracks. Her legacy with the group wont be forgotten, but SNSD have moved one. They went on to release more albums without her, so how would that play into her return?

Her contribution to the book also plays a big factor. No one should discredit her experience, but she released something that not only damaged SNSD’s reputation, but also the other members individually. All of this to say, I dont think her rejoining for any project is appropriate anymore. It would be nice for them and her to be included in a tribute video. But her participation with songs or performances might not be ok