Oh, if you put me in charge of how the story ends, I would absolutely go with allowing the player to find a fix to the engine using one of the several possibilites that are currently in the game that seem like they could work. I'm just trying to temper my expectations with some degree of realism- unless there's a lot of dialog that was cut or something, you'd have to do a lot of new voiced lines, program and animate dialog, and so on to make an ending like that. It's not impossible, but I genuinely don't know enough about the process to know how likely or realistic it actually is to expect that. I think something building on the Avernus ending would probably be a lot easier to implement in a satisfying way- it'd probably only require a few extra lines of dialog at a few key points and an epilogue after the game to work, and if you did it right, you could still pull off an ending that's at least bittersweet instead of just horribly depressing.
Isn't that what Avernus ending is supposed to be? (Especially after patch 2) More hopeful ending where you Karlach and possibly Wyll go to solve the problem themselves. Anything more would require retconning her whole story which is very hard task, if possible at all without burning through too many resources. Especially considering she wasn't supposed to be origin in the first place but was late addition
