You'll just have to talk around the mask! It is, after all, an EMERGENCY situation at that point, and you might have to innovate if the pubs don't explicitly cover it.
First, you have given no reason to expect a sudden depressurization. How many have you experienced in airliners (probably a few less than I have in military fighters)? Pulling the mask away from your mouth for a few seconds to talk will NOT mean instant death. You may even find that you are adequately understandable through the soft-cup mask and the hand mike.