With this kind of ending... I don't see room for a second season.
Maybe an OVA. Maybe.
I think that the ending is fitting. One of Simoun's core messages is that life goes on even when it seems like it will (or you wish it would) stop. The rest of Chor Tempest has no idea what really became of Aaeru and Neviril - why should we? They don't know where Amuria went, either. Heck, they may not even know what happened to some of the ones they went to the Spring with. Considering how life
really goes, I think we got a lot of insight into how everyone turned up. Their lives aren't resolved yet, and hence the story itself shouldn't be resolved.
Plus, it gives us way more stuff to argue over
