As airways sad, it depends what is your main goal,
but if I got this right, in this situations I always close access to CP for almost all user groups, you can limit their access, super admins have always access. I guess your site is already in offline mode, even not necessary.
[EE2] In your member group preferences (select your member group > edit group) you have “Control panel access” tab, you can set there ‘No’ for groups you don’t want to access and change something. You also have ‘Site access’ tab.
I hope this helps