A spoiler-aware overview of the known ending routes and the decisions that can close them off.
How endings work
The ending route is shaped by major choices, alliance decisions and the state of the final confrontation. Treat late-story dialogue and commitment choices as irreversible until you have checked the consequences.
Known ending routes
PowerPyx documents The Turncoat, The Folk Hero, The Patricide, The Knyazmaker, A Hero They Deserve, Together Forever, and the time-out ending. Some are tied to defeating Brencis, while the bad ending is tied to allowing the available story time to expire.
Before the final stretch
Keep a manual save before major allegiance choices.
Finish optional objectives that matter to your preferred route before committing.
Do not assume an early ending has the same requirements as a final confrontation ending.
A practical replay plan
Use one first playthrough to follow the choices that fit your version of Coen. For completion work, retain a pre-commitment save and branch from it rather than attempting to recover a locked route after the fact.