https://www.polygon.com/2018/9/14/17860268/nintendo-switch-cloud-saves-lost-subscription-lapses

Nintendo is finally rolling out cloud saves for the Switch, which will be included in the upcoming Nintendo Switch Online. The majority of games will automatically have their saves pulled into the cloud, with a few exceptions such as Pokémon: Let’s Go! and FIFA 19. While this makes for a good back-up, there’s the question of what exactly happens if you forget to renew your subscription?

The Nintendo Switch Online FAQ implied that cloud data would be lost the moment a Nintendo Switch Online account became inactive.