Great question! I also stopped drinking during treatment, but started again while just doing herceptin. I actually went to a wine tasting the night before one of my herceptin treatments (I totally forgot) and freaked out. My oncologist laughed at me and said I was fine.
I have a few glasses of red wine throughout the week, or a beer here and there, and my oco is fine with it. and I think it's a great stress reliever