Or once they're finished using her for whatever they wanted, they kill her. Or even indoctrinate her into thinking she *should* be the last avatar so that she willingly chooses the end the cycle herself when her time to die comes.

He ran fast and dodged well. She was definitely aiming for him all the way.

Having an heir who "officially" inherits the throne doesn't mean much unless the heir can win control/loyalty from the military and whatever other factions that are needed to subdue the popular revolution Zaheer kicked off.