I would say at least 50 years honestly. The amount of nostalgia that can be mined here is like Star Wars, almost never ending. They can "remake" games over and over, create newer version with more features (very, very slowly), and introduce new customers, rinse and repeat until that well is fully dry.
Pokémon is a 25 year old game that has made more money than any other IP out there. It's gonna be king for a while. Especially when there are toys, games, films, tvshows, etc all coming out.
hopefully this funds more Metroid and Wario games.