Even if you complete the quest that enables Doctor Henry to eventually find a cure for schizophrenia, Lily doesn't have an ending slide that reflects this outcome. Therefore we have to entertain the notion that Lily is never cured and continues living with her condition. And in which case, regardless of the Courier's actions, that in every possible scenario it is a mathematical certainty that, provided Lily lives long enough, she will either stop taking her medication or find herself in some set of circumstances where she doesn't have regular or any access to her medication and will inevitably be overtaken by her schizophrenia. So it doesn't matter what ending the player chooses for her, they all lead to the same place in the end, only the journey there is different.
