updater.sh returns with exit code 0 when failing to download user.js file, for example, when no internet connection. The assumed result would be to return a non-zero exit code. This way, if the updater fails, one can retry after some time.
One way to solve would be by explicitly returning 0 at the end of update_userjs function when it completes succesfully and calling update_userjs || exit 1 to exit when the update_userjs function returns non-zero value.