They shouldn't have to shut down the servers to update the app at all if it was only user-side changes like text; more generally, any changes that wouldn't leave database discrepancies between playing the game on different versions should not require servers to be off to update. Essentially all current major issues with the game don't have to do with the gameplay mechanics themselves, and so updates that fix these issues should be fine to release without any server downtime. At worst, if the way the app communicates with the game server changes, then downtime would be needed because they'd need to change server code. On the flip side, if they do make any changes to the game mechanics, the app itself shouldn't have to change very much, if at all. Kind of the point of having a game that relies on server-stored information is that the app itself is just an interface for the user to interact with that data.