Mavis tells Kana very clearly that she must erase and destroy her own soul in order to regenerate and awaken. After telling her that the soul/spirit was completely destroyed, Mavis was able to revive her soul/spirit and come back to life without any problems. We know that Mavis' Thought Projection Body is only her spirit/soul and for all intents and purposes is a ghost. Spirits and physical bodies are interconnected in Fairy Tail, which is no more powerful. When Acnologia's soul was completely destroyed, her physical body was also completely destroyed because they were both connected. The same would have been true for Mavis, but since her body is immortal, it would not have been destroyed when her soul was destroyed, so why did this happen? We also know that Zeref tried every way to kill himself for 400 years. He could have learned about body dismemberment from the R System, the Ars Spell, the Corpse Dragon Slayer Spell and more. Zeref also knows that Existence Erasure cannot kill him. So it is strongly supported that Mavis and Zeref can regenerate by having their bodies and souls' actually higher because remember the statement that none of the demons can kill zeref.
For the scale in Vsb, you can look at the regenerator in zeref's basic switch and see
https://vsbattles.fandom.com/wiki/Zeref_Dragneel