It does seems a little dumb from a IF writing perspective to make an umavoidable punishment for players who made a decision several books ago when none of this information outlined was available.
It's also a terrible decision from from a role-playing game perspective. This is like if the only ending Renegade Shepard, Demon or Necromancer MC from Wrath of the Righteous, Closed Fist MC from Jade Empire, Heretic MC from Rogue Trader, and all other games with an evil option would have is only death.
If Anon actually go through with this, then he would've committed two cardinal sins for a creator in my opinion. Daring to moralize to the reader/player, and being
boring.
It's one thing if the MC is set as a goody-two-shoes from the start, like any other linear JRPGs, then condemning evil isn't really moralizing, just the message of the story, but if a game allows an evil path, you simply cannot treat that path as the 'inferior' path nor condemn the player to an unavoidable death.
If this is to be a story of the triumph of good over evil, then the first evil act of the MC should be swiftly punished, rather than let to rot and fester until the fifth installment of the series.
Even if the scene itself would be hilarious to read, and I know Anon have the skill to make it so, narrative-wise, there's nothing interesting about an unavoidable death. I have no qualms if death is one of the ending that awaits a Demonic Cultivator MC, it makes sense after all since demonic cultivation is looked upon with scorn in the setting, but it should not be the
only ending available.
I fully agree that an 'evil' path should come with its own downsides, though. I LIVE for the consequences of my actions. Like POMA irreparably destroying your relationship with Ai, maybe take away having Eldra as your mentor as a possibility, but in exchange they should get something equal to that down the line.
If anything outside the heavenly order is 'corrupted', then lean into that. If ascending becomes impossible, then let them be the first to
descend. If that's supposed to be impossible and not even the most ancient beings are capable of such a feat, then remember that main characters are
supposed to be special.