Unless there's new info that I didn't see, VPI-UVA wasn't cancelled, just rescheduled for later in the season. The ACC moved the Duke-UVA game up to the end of September so that UVA wouldn't be sitting around until October waiting to play. So we haven't cancelled any games yet.
You do bring up a good question about what will happen if some teams do have to cancel games, or if some cancel more than others. I assume there has to be some assurance of "good faith" to avoid your UNC scenario, and if teams are making their best effort to play, I assume they'd get their full slide of the payout.
The UNC scenario is a larger version of "how fair would it be for the Big 10 to only play 8 games and then get a team into the playoffs" question. The ACC may just be counting there being obvious choices for the ACCCG such that a few cancelled games won't matter. If Coastal Chaos/Circle of Suck comes into play, things may get interesting.
I'm also intrigued by something I saw on the crawl during our game but haven't seen followed up on, which was some ACC document that VPI released (for some reason) saying that the league had some conditions under which they would discontinue the season (such as falling under 8 teams playing games). So far, at least, that doesn't seem imminent, unless the wheels really come off as the season progresses.
JRjr