Rush, on the radio just now. He explains: Sponsors are both local and national. The 600+ stations sell their own ads, and Rush doesn't even know who those local sponsors are. These sponsors don't cancel their ads on the station, they just put in an order that their ads not run during the Rush time slot. Things like this happen every day, and not just to Rush. "It's part of the business," but because there's attention to Rush's current problem, there are reports of these local advertisers putting in these orders, and the local stations don't even lose any revenue.
The left is just putting out propaganda, trying to create the impression that Rush's show is over. They are portraying local advertisers as if they were Rush's national advertisers. The 28 advertisers, at the 600+ stations, amount to virtually nothing in what is a pool of something like 18,000 advertisers at the local level.
He doesn't talk about how many of his national sponsors have canceled, but there must be some, because at one point, he talked said "2 of the sponsors who have cancelled have asked to return... one of them is practically begging," so there must be some.