I think it depends on how much how Gaius survived matters to the story. If it involves something like... taking the Heart of Sabik with him, then they'd better tell it.
The other thing to consider is how Gaius got to Ilsabard afterwards. Lore Book 2 has finally revealed what happened in Gyr Abania between Operation Archon and Stormblood. Shortly after Operation Archon, the XIIth Legion invaded Gyr Abania and took over the remaining XIth Legion members there including the Skulls. So Gaius would have had to make it through a region where everyone would hate him if he was discovered...