Well if its 'impossible' nothing will help so ill insult all i want, wont take your word for this anyway who the fk are you know what i mean
I'm a software developer.
1) When the game is updated the client (the software installed on your phone) needs to be updated. It is impossible to update the client without closing it. There are server side updates only but, these kind of updates (with new content) require a client update.
2) They could let your client be connected to the server while they were they doing the server side updates, and you could update the client later when you wanted. This would be a very bad idea as your client version would not be the same as the server and all sort of unexpected errors could happen.
You already know that you will not be able to access the game while it is being updated, and yet you insist on not spending your stamina the day before? You have no one else to blame but you in this case.