Hopefully, there’s a loophole somewhere because it feels really unfair that after being separated all this time, that their reunion as a family would have to be cut short because Amara would have to die.
It’s incredibly sad, no doubt about that, but the fact is that Amara wasn’t supposed to be saved in the first place. “My water can heal only those whose destinies have yet to be written. Your mother’s fate has already been sealed. She will die.” Amara’s fate was supposed to be to die that day, and her fate got postponed, but you can’t avoid fate for forever. It’s like how the Seer said that Rumple’s actions would leave his son fatherless, and it took a while, and a more convoluted route than Rumple had assumed, but it DID happen eventually.
Amara dying now would be restoring the order and balance, which should never have been disrupted in the first place, all those years ago when her sons saved her.