While mixing on headphones is possible, you can't beat having both a great set of headphones AND a great room.
If you truly want to produce industry-quality mixes and masters, it helps to listen on speakers too. The truth is, a lot of listeners will be using speakers, so you need to know how your mix/master is going to translate.
You also need to be aware that most headphones are not perfectly flat and have their own inaccuracies. This is something we will talk about at the event too.
So, while it's certainly possible to achieve good mixes with headphones and lots of testing in the car, everything gets easier when you have an accurate listening environment, in addition to a good set of headphones.