I think, instead of the weird RTD-Can't-Stick-To-An-Ending "let it go" metacrisis 'resolution' it would have been so much more satisfying and bittersweet for them both to go "yeah, we know this will kill us eventually, but we'd rather be complete and happy than safe and empty"

It would add a lot more to the trans plotline too. If The Doctor were to be like "the metacrisis is going to kill both of you eventually" and Rose was like "Maybe. But we don't know how long that will take -- it could be a whole lifetime away. I'm finally myself and I'm not letting that happiness go."

How sweet would that be? Being openly trans is dangerous. It could get us killed at any moment, but we'd rather spend our short lives complete and happy than deny who we are and be miserable.

and then we could have a SJA style DoctorDonna spinoff where she and Rose use their unique part-time-lord abilities to save the lives of ordinary people on Earth