A McAulliffe victory of ~8-12% wouldn't surprise me at all. There seems to be consistency with Democratic margins in Virginia now. Biden won by 10%, Warner by 12%, and Northam by 9% in 2017. The only significant outlier to this was Kaine's 16% win in 2018, and that was against the worst possible Republican candidate (Cory Stewart). There's a slight possibility that Youngkin could pull off an upset, but it is very slight. McAuliffe will run up the numbers in Northern Virginia, Richmond, and the Tidewater area, and that will be enough for him.
Yes, but that gets him to +6, not +12. For that, he needs the outer suburbs at Biden levels and/or a better-than-Biden performance in the rurals. Also, Youngkin has personal connections to VA Beach, so I don't think Biden/Northam level support in the Tidewater is assured. McAuliffe still wins if it turns into a true NOVA vs. everyone else race, but it would be an unimpressive margin, perhaps +3.