As an additional point of reference, pulling a stinger like they did after a "we may never meet again" ending, only to end up ignoring that person, is appallingly bad form. Rather, I don't think it's ever been done. Even if they ultimately subvert it (looking at you, Digimon Tamers), it's still a possibility that needs to be addressed.
Again, for the entire run of FFXIV it will be impossible to prove that CT is an isolated story, but all-too-easy to disprove. I personally would like to believe that the last prince of Allag is too important a character to be simply written off for a message about hope (especially one that contradicts XIV's other messages on hope rather spectacularly), seeing as there's still so much Allag left to deal with.
It's also a point worth mentioning that Desch, the character G'raha was loosely modeled after, did seal himself in a tower because of his destiny (and presumably died), but was later let out by the ghosts of Doga and Unei so he could continue to help the Warriors of Light. So completely cheapening that sacrifice would actually be entirely appropriate FFIII fanservice, and could even be the real way for the tower to be a "beacon of hope."
I'm not expecting any sort of continuation any time soon, just felt like sharing my (completely batshit) findings while they were still relatively fresh.