Sure you can have one offline and one online with the same email and different passwords. If you’re offline, you’re offline. Offline you could use my or Bill Gates email or Elvis. As long as it’s a syntactically correct email, i.e. has the dots and ats in the right places, there’s nothing more we can do to validate the email or verify the password when you’re offline. You’re offline! No Internet.
As for point 2), the short answer is that you should not walk away from your computer with Windows logged on.
If you do, you’re lost anyway. If someone else has access to your computer, with your permissions, it’s no longer your computer so to speak.
Please read http://www.axcrypt.net/blog/leaving-computer-axcrypt/ for a longer discussion and explanation why this is so, and how AxCrypt mitigates this and other risks.