There is no way you can self-assess BAC which is why most pilots just used the 8 hour rule in the days before DAMP testing. I would guess thats what the Virgin pilot did. The fact that he is now working for another airline demonstrates that CASA don't just take your license away and that Virgin were a bit harsh IMHO. As I said it could happen to anyone except if you didn't have anything to drink at all on an overnight which would seem to be the only guarantee that you had zero BAC. For those who do like to have a drink then at least the home-use breathalysers are some form of mitigation.