Negotiation

Marlena considered it. 

Seeing what her daughter was thinking, Regina frowned in disapproval. "Don't even think about it! I still need you alive. Besides, so what if you gave your life for her? She would never be happy living, knowing she is alive instead of you. She would be sad for the rest of her life. 

That, and the mother queen's existence had no use for Hades if Marlena was not alive. Who knew what that demon would do out of spite? 

Luckily, Marlena didn't insist once she thought about how heartbroken and guilty her grandmother would be. 

"What can I do, Mother?" Marlena clung onto Regina's arm, her eyes brimming with tears. "You must have a way, right? If even you are alive now…if I was dead too and I am here now…there has to be a way, right? Right?"