From my experience you'll receive a partial refund - and in some instances like inexplicable overspending, etc. - you won't receive anything. This may be an exception given a full sitewide outage, though

How is money even being spent if users aren't viewing the ads?

That's because they were some smaller places.

When you've more-or-less monopolized a lot of the web's content sharing you get to tell your clients to pound sand. Where else they gonna go? Twitter? The incel white supremacist dollar is not what advertisers call "the good dollar".