I am in a similar situation as you. My commute is about 11 miles. I have often contemplated ditching one of our cars, but I haven't really been doing this long enough to know if this is biking to work is a sustainable option for me long term. I've only been at it for about six months, riding 2-3 times a week. It's kind of a nice relief when, after riding a few days in a row, I can drive and just take it easy. I suppose, like you said, if you had to do it then you'd do it. Right now I don't have to ride everyday, so I don't.
If I can ditch one of the cars I'd save a lot of money. My insurance would be halved. Fuel saving is substantial, as well as maintenance of the cars, registration, etc.
We also have three young children who need to be driven everywhere, A second car does come in handy when we have each child has a different place to be at the same time.
I, too, would be interested in hearing from others about their experience going from two to one vehicle.