It’s not an open ending, it’s indoctrination theory in the making 2.0.
The only solution is that CDPR will go with full Bethesda and release its version of Broken Steel expansion (FYI it was 3rd expansion for FO3 so they took their time).
Right now those endings are as open ended as TW3. You have 6mo of grace period with rapidly progressing Parkinson’s Disease with unknown treatment, which is confirmed by top scientist in this world in neurosurgery and top AI.
Lizzy Whizzy - Fully cyberized with partial organic brain. Went crazy.
Adam Smasher - 95% cyberized; only the brain remained. Already insane, already had fantasies of being weaponized, confirmed that gruesomely mauling people to death was his pass-time. No sane person willingly wants to become a robot.
Cyberpsychos - initially thought and theorized to be a result of PTSD or Traumatic experiences peaked by neural implants. Turns out to only be half-true, because just over half of the Cyberpsycho quest cases turn out to be ordinary people whose brains simply couldn't handle the stimulus caused by cybernetic augmentation.
Maelstrom - Not one of them is mentally stable, yet somehow remain 'functional' despite heavily augmenting and replacing parts of their bodies and brains.
V - The first fully cyberized human with a synthetic brain to not go insane, not to be insane prior to the transition, made possible due to their strong desire to survive at all costs, and having been Engrammed in the process. See: Major Motoko Kusanagi of GITS.
There's the cure. NUSA are implied to be appearing in multiple endings.
Essentials to remaining mentally sound in order to transition from organic to full synthetic: Strong will/"Already Insane", Engrammed.
Sequel potential, commence.