The secession of Iato has been planned for RL years. It is the culmination of what Riombara has been working toward since the end of the Last Invasion: the refounding of IVF under its last ruler who was not a traitor to humanity. This would have happened whether Enweil was at war with Riombara, at peace with Riombara, or dead.
Now, that said, I will grant the timing's not the most astute.