If you give me an empty say in an empty paragraph, I presume
that you're done writing, and turn my attention back to
everyone in the room. Hence, at the end of a paragraph, two
empty says in a row will first save the paragraph, then
leave writing mode. You can also leave writing mode (without
saving the current paragraph), by saying "abort" or by leaving
the room. (Therefore, if someone has locked me into writing
mode and then logged off, you can take me out of writing mode
by killing them or moving them.)