iHeartMedia is probably too big to fail. Their shareholders will sit this out. They are the 500 pound gorilla in the radio room, and are looking forwards with IHeartRadio, custom streaming, etc. This isn't the first time they faced the wolf at the door and came away still running....
Radio revenue is still tight. These massive companies are keeping MW afloat -- they put various low-revenue formats on them and use them basically as loss leaders.
If the IHeart and other big co's busted we would possibly see a bunch of local owners buying up stations, owners who would then slough off a lot of AMers, selling the land to developers, and the MW band would have much fewer stations. Some DXers would cheer until they realised that eventually their DX targets would also be gone. There would also be more religious b'casters on the air, which many people don't like. But they have the will and the money.
Do you really want Brother Stair on every 1 kilowatt AMer in the US? Then pray that IHeart goes under. :-) I'm exaggerating, of course. But who really has the money to potentially lose on a small AM station in a suburban market? Being part of a cluster keeps many of them afloat.
FM would still be just as overcrowded as it is now. Perhaps moreso.
Could get interesting...