Hard to say for sure but I have two possible theories for why Syla said that. 1) She didn't actually believe he wouldn't use it, it was just a comment to make light of the situation which seemed pretty central to her nature as she always made light of everything, never gloomy or serious. 2) Given that she called him "Indi", which sounds like an endearing nickname one might use for a friend, it's possible that Syla and Indra were actually very old friends that go back centuries or millennia but he gave himself completely to his patron so when Syla became a target of the 2nd, Indra could no longer resist or cared to...his identity was entirely consumed by his patron. This is something Ella warned the MC quite early in the game...she said the monsters want level 5 superhumans and to be prepared because they would come to claim him. Indra or this concept of being an incarnate is probably what that means...and the MC and companions will probably have to contend with their patrons trying to claim control over them at some point.
I think this fits dead end 43, be an apostle or arbiter the eye takes over Mc erasing his identity, it also fits the descriptions of the big three:
Malik is completed but kept whole by faith, a reference to his morality keeping his identity
Henri is ascended yet unborn, reference to the fact that whatever is supposed to take over is ready to be born at any moment since he is already ascended
Bernhardt is old but unbound, i guess this is about how corruption piles up the more time passes, so it should bind the will of the superhuman to whatever being wants to take over.
Yet each one somehow found a way to keep the process at bay, for decades now.