Also, as an add-on to my previous post about aether returning to the land and empowering the primals again - given that the Twelve's sealing magic failed, it's very possible that the remaining aether dissipates either into Bahamut or into the ground - I'm willing to bet the latter because you see the remaining magic falling away. As the scale of the sealing spell is probably one of the largest spells we've ever seen (expanding at it's largest diameter from Limsa Lominsa to Nine Ivies) it's very probably that the amount of aether returned to the land is in huge amounts - enough to empower the primals again to regain corporeal form.