You can not sacrifice that which you do not own. You can not buy power with that which is another's. Alcyoneus could not be risen save by Marie Lévesque's willing offering of her life, and the acquisition of a fragment of the universe that was is no different.
Here's the problem. Thanos stands upon the altar, dragging Gamora by force. He wishes to cast her off it to trade for the Soul Stone.
He is a fool.
Marie Levesque stands in an underground cavern, looking at a bulb holding the doom of the gods. Her patron wants her to give her life to resurrect the death of Death.
Gamora can stands on the altar, her death the key to Thanos destroying the world.
Marie Levesque's daughter is held hostage, and she stands helpless within Gaea's dominion.
Gamora can't escape.
What can be done?
A future lies ahead of both the Guardian of the Galaxy and the Daughter of the Wealthy One.
The world is at stake.
What can a mere individual do?
Even when death is inevitable, choice will remain. The manner of death, how one greets one's imminent demise. The purpose of death, what one judges worth traversing for the last time the River Styx. The meaning of death, in the end, how one interprets the departure from the world of the living.
Choose.
Hazel and her mother rejected Gaea. Neither died for her cause. Neither of their souls were given onto the goddess.
Gamora?
She is not Thanos' daughter. That is her choice. No one can own you save for yourself. She rejects his claim. It is her right. She is Gamora, hero, not Gamora, pet killer. She is a Guardian of the Galaxy, not some trophy from a ravaged world. She will not die for Thanos.
And Thanos?
He forgets it. He forgets that he had no right to decide for the countless lives of the galaxy, of which Gamora is one. He forgets, has never learned, that his only power is the power of domination, to with force cow, and that such power is weak. It only takes a single refusal to break it. And when Gamora has nothing and everything to lose? That "no" is easy.
"I can walk." Says the woman.
It is allowed by the fool.
The woman walks freely to the edge of the precipice.
The surest escape from the mundanity of villainy is to teleport into the tragic realm, and this is a tyrant who fancies himself a tragic hero. He hopes that his daughter will not force him to make the last step.
Gamora takes the leap.
Who sacrificed?
Gamora is Gamora's. Gamora gave her life for her ideals. Thanos was but the ferryman. Twas Gamora who sacrificed herself, not the Mad Titan. The Mad Titan could no more claim mastery over her than he could any other being, no more than he could consider himself Rocket Raccoon's master, or Wanda Maximoff's.
Gamora falls. Then she wakes in water, a golden stone in hand.
She has been judged worthy.