I can't shake the feeling that Gaius was actually meant to have been killed off for real, his death was just left vague as a stylistic choice. Though to be fair, his death was very reminiscent of Rufus' 'death' in FF7. Most people assumed he was dead as the scene ended when he was apparently caught up in an explosion...only for him to turn out to have survived when the canon material was expanded. This was, in no small part, due to his popularity.
So I find myself wondering: was Regula intended to play a bigger part in the story? For someone with such a memorable design he only showed up briefly in the MSQ's and then he ended up playing a major part in the Azys Lla side quests...going so far as to sacrifice himself and fight alongside the Scions and Warrior of Light. He also fully intended to return to Garlemald empty handed, deeming the devices in Azys Lla far too dangerous and volatile to take with him.
He was portrayed as honourable, willing to team up for the greater good and he had strong ties to the Emperor. Yet his strong ties were only touched upon in passing and then were never mentioned again.
Could he have been the original intended route for us to get to Garlemald? Only to be replaced with Gaius once it was decided that he would be making a return? I'm torn on his appearance, honestly. Gaius made for an interesting character. Yet he isn't likely to remain as he was back in 1.0 and 2.0.
Either way, I think 4.4 will likely give us a lot of information about the former Emperor of Garlemald, the current Emperor of Garlemald and also fill in the blanks in regards to Gaius van Baelsar. I also suspect we'll learn more about the Ascians as it seems like Elidibus isn't operating alone in the region.
As for Fordola, I do like the idea of her using her newfound powers to aid in Gaius' cause. She did seem to hold him in fairly high regard, after all. I don't think she'd be a good fit for the Scions in the long run due to the bad blood between them. I also suspect that she does not necessarily want to remain in Ala Mhigo and if granted freedom she would slip away elsewhere.
I think she'll be involved in 'outing' Zenos. Perhaps by sensing something amiss or having a vision if she catches a glance of him in his elezen form.