I can explain why Barbuda dying is important.
Barbuda is the only reason Gidget is alive. I sorta made up some background on nimbats they are ageless guardians that don't die until whatever they are protecting is gone. Basically the years they spend guarding catch up with them and they die. Gidget is guarding Barduda and the temple but both are going to die. The temple is only being held up by Baruda and when he dies the temple falls and then gidget dies in turn as she has nothing left to protect. The only way to save Gidget is to have her protect something else of importance, namely the wielders than she won't lose purpose when the whole temple crumbles.
She is not immortal just ageless so long as she has something to protect.