Yeah, no retcon is needed for her to be given a happy ending/fixed engine optiin, not sure where this is coming from. Its been suggested before here but as a suggestion it could be as easy as having two extra dialogue options. With the gondians and dammon with enriched. Thats the easiest route*
Also id think everyone would agree that if a way to fix her was a implemented. It would be AFTER the gortash fight. Cause god damn sam did an amazing VA for that scene. Theres really nothing wrong with getting a fix after *experiencing no hope left * scenerio
Prime example in the game. You assume as a player wylls father is dead, gone, cannot be found, doomed to die as you seal his fate. By refusing to renew wylls contact. Everyones sad. Shocked and dispair sets in. Then by sheer player enginuity (by design by the devs) You can STILL find wylls father and save him defying mizora
Which is always a good feeling
With retcon I meant concept of her character, keeping in mind she was not origin etc etc. "Happy" ending invalidates the option of turning her into the mindflayer (she's not suicidal so no reason for her to do that) and the mindflayer option is in game from the begining so her making the sacrifice was always Larian's intention (or at least the option to do so, why only her is anyone's guess, but considering rest of her endings the answer is fairly obvious). So for the option to not stick out like a sore thumb and be completely pointless, they'd either have to delete it which is not likely or give the option to the rest of the companions, for example ultimate face turn for Astarion, way out of curse for Shadowheart etc. Now that's a lot of work and even more changes to the story
