Originally Posted by
Berteaux_Braumegain
I think they're referring to how Hydaelyn's backup plan would be for the people of Etheirys to flee elsewhere, which would lead to Meteion destroying the world and thereby the other reflections of Etheirys. Thancred, notably, was not entertaining the possibility of not fighting Meteion because he was worried about Ryne.
That said, if Hydaelyn is tapped out on power and the Warrior of Light can't defeat Meteion, I'm not really sure what else the backup plan could be. It's clear Hydaelyn would prefer that they can defeat Meteion, but she left an out for the people of the Source so that SOMETHING could survive in the event that result wasn't possible.