I allways felt the main heros were supposed to fail their quest if it weren´t for the subtle influence of more humble persons (Vaan,Penelo,Dalan,etc...).
If weren´t for them Ashe would be dead,Bach would die with people blaming him forever,Larsa would not become emperor and nethicite would win over.
Because they were destined to.
Only something from the ghostly realm could change timeline.~
They would follow the destiny writed for them from the gods laughing on they heavenly abode.
(Pay close attention to this last words).