I don't think the gas will come out of the ground in a large amount . the mush top is going to act like a cap.Its not going to collapse into a giant huge hole. It will look more like a water/oil lake.The well water wont be worth drinking anymore in the area. The land will be shit for thousands of years because of the gas coming out of the ground.Nobody will be able to live anywhere around it , or down wind of it.