You misunderstood me.
Right before you enter the final chamber, where Lucian is, if you have Fane on your party a voidwoken will appear and ask you to, when Fane ascends, return the Eternals to Rivellon.
If you tell him that you will do that, you can't get the regular Fane ascension ending, because when he ascends, he will bring back the Eternals, and with them, the God-King (which is one of them).
So unless that specific conversation is meaningless, it is your problem.
On the other hand, if that conversation is in fact meaningless, then you're probably "stuck" until these things eventually get fixed.