Are there any examples of a demon or devil ascending to become a celestial in lore?
I know the answer in my own campaign, but it seems like most fiction (D&D related and otherwise) seems to assume that you can fall, but not rise. But, as I said before, it will depend on the DM. Could it theoretically happen? Perhaps. But if over the millennia, only a single celestial or two have fallen and no demons/devils have risen, then it's as close to impossible as to not matter.
Which has little or no relevance to individual campaigns. In some campaigns Asmodeus could be redeemed, in others orcs are born evil and are simply hard wired that way. Neither is right or wrong IMHO.
But as I said earlier, maybe it's not a question of success but the attempt. If that ogre is trying to smash you into goo so he can use your remains as a sandwich spread it may be a moot point. It's one thing to try to redeem someone when you're not in combat, but whether that's going to be an option is largely going to depend on game style. I've had NPCs that were being groomed to be the BBEG that ultimately became allies, but it was due to repeated and continuous interventions and conversations not just a one time conversation.