Well, eBay would tell you to use the correct form, and report the member as having an invalid email address. Usually within 24 hours they will be NARU (banned).
As for what you should REALLY do... if you feel comfortable dealing with someone you can't contact, and eBay could ban at any time, then go for it. Myself, I'm very wary of this kind of buyer, and tend to get them NARUd. They can't retaliate with feedback if that happens, so you have nothing to fear other than wasting a bit of your time.