Pending insurance appeal, debt goes to collection


Briefly: a year ago I was sick with Coronavirus on Thanksgiving. Next day on Friday, went to the only open Urgent care. It used to be previously in network. Turned out, it wasn't in network any longer, and insurance didn't cover it. Long story, the urgent care didn't send me any bills till much later, I wasn't even aware that the bill wasn't covered. When I found out, I complained to insurance and phone representative said they were going to look into it. I don't know if that person filed an official appeal, I haven't got any denial of appeal mail. Finally, the urgent care sent me a bill that said FINAL. I called them and also typed an appeal and faxed to the insurance. The insurance said it will take up to 30 days to make a decision. The Urgent care person said on the phone that she had no power to stop it from being sent to collection, in other words, they were not going to wait for 30 days.
Its over $300, I don't have extra finds to pay it and I don't think I should, I have lots of other bills that I do pay.
What will happen if it gets sent to collection and then insurance decides to pay it?