From Nintendo's side, easily Fire Emblem.
Fire Emblem was a dying franchise, mostly because of it's stuborness to evolve and adapt new mechanics to make it's games better than just good. It's thanks to the threat of death that the developers said "what the hell" and actually decided to take a chance and do something they wanted, instead of being held back by what the old fans expected out of the franchise.
From Square(Recent years): Easily FF 7 Remake. FF 7 R was the first time since FF X, and maybe even FF XII, that a FF game felt this perfect. FF XIII and FF XV really manage to tarnish the brand name, but I feel like FF 7 R managed to clean it up alot, and probably restore faith in the franchise.
Sony has always been weak with it's first party offerings until the 7th gen, given a few exceptions. So most of it's beloved franchises never really fell from grace.Yet, at least.
MS is hopefully in the path to redemption because they are a huge dissapointment first party wise.
RE 7 basically brought the RE franchise back to life.
Megaman 11 also almost single handedly revived the franchise. You could say that the collections did that, but for me those collections only showed Capcom the lingering and growing interest in the IP. Megaman 11 basically solidified that claim by being a new entry that is, at the moment, the third best selling entry in said franchise.
There is probably alot more, but I'm too tired to think about that now.
My (locked) thread about how difficulty should be a decision for the developers, not the gamers.