I will be going out of town for about a month. If the CA MFC processors need anything from us, do they contact by email or regular mail? I just don't want to get into a situation where they say in a regular letter please respond in fifteen days or your application will be terminated. If it's by email, then no big deal.

It doesn't work like that. If they need something, they will call. At the most, your application will be delayed, but not terminated.