Clevernick, I wrote you a really nice long response, and lost my connection as I was posting it, rats rats rats
Suffice to say: thank you for taking the time to answer, and I think your point about cutting out being the only action a dom can truly control on line is extremely valid and interesting.
I do think he needs to consider when it should be used, and we must talk that through. You are right that communication - and the chance to communicate - is the prime necessity.
Just on your general comments - I appreciate that some subs can be pretty unsub, but I am extremely obedient and docile (no, Wolfy, I really am!!). So if I don't do something at once then perhaps some more gentle persuasion first would be reasonable... especially since he knows that cutting off the conversation is, to me, the worst punishment I could get (on line). I will talk to him about that, too.
Generally - guys, what can I say - as helpful and thoughtful a response as I could have hoped for, and has given me food for thought.