Anything related to the 7th Umbral Era will be gone and I would assume the Primals will be reworked into the new story somehow. I mean like you said, can you really imagine an FF game without Ifrit or Garuda? The Moogle fight really has very little to do with the 7th Umbral Era directly. The Garleans just wandered onto Moogle turf and got messed up, they've been seen in The Black Shroud in the main storyline.