The problem was not the earthquake, so much as having a single source of power for all mankind. As that seems to be G'raha's end goal (but apparently not Salina's), I'd say we're exactly repeating history. Given it can "only" be opened by the royal blood, according to in-game sources, if you can accept the possibility of it being opened again without the royal blood, then the royal blood never needed to be preserved inside it to begin with. Not even Alexander can sort out that paradox.

Anyway, my point was that having a single anything in which you place all your hopes invites disaster, be it world-powering power sources or the one person on the planet with any semblance of individual agency. This may be my Libertarian side showing, but I think the story as it is now could easily be rerouted into an examination of why Eorzea needs to be able to save themselves without counting on a Warrior of Light to do everything for them.

tl;dr: The story could only become more interesting if we died.