What happens if u don’t update for a month or longer?

Nothing. You'll just get a warning of new updates but nothing happens in that period.

In time you might end up with non-working apps because they demand a certain iOS version, but that'll take a long time to happen, not just a month.

You will not be able to update new apps... and you there are new apps on the apply store you won’t be able to download them because your iOS is outdated and need to be updated...

You will often get notifications to update. Remember, it is always good to stay up to date for security!

It will download faster, since fewer people are trying to get it.