The fetus in not autonomous. It's 'personhood' is dependent upon the mother's personhood being willing to sacrifice her body to it while it's developing to the point where it's body can survive on it's own. If the mother is not willing to do that, than either the fetus' presumed autonomous personhood is ended, forever, or the mother's actual autonomous personhood is usurped by force, at least until the child is born.
It's not about physical survival, it's about autonomous personhood. If I enslave you indefinitely, and make you do my bidding all the days of your life, you could survive, but not with autonomy. Which means you will never get to live your own life, you will only be able to live the life that I dictate to you.
Is that living? Sure, you'd survive, but for what? What's the point of existing without free will? Without the autonomy to be yourself?
Everyone thinks the abortion issue is just about survival. But it's not. Not unless the fetus could be removed to develop in an artificial womb. But so far we can't do that. So for the fetus to survive long enough for it to become an autonomous being (and thereby claim it's personhood), it remains subject to the autonomous personhood of it's mother because it can't survive outside her womb. And if we force her to carry that fetus to birth (so that it can gain it's own autonomy), we are usurping her autonomy in the same way we usurp the autonomy of a slave. And slavery is illegal in this country, and in most countries of the world for good reason! Because even though it does not end one's physical existence, it does end one's personhood.