The End of the Source Chain
The young men were unable to get in contact with Dan Turner, and they subsequently lost contact with Art Bell as well. Tragically, Bell died of a heart attack just three weeks after their final correspondence. With no more sources to draw from, the young men were forced to shelf their investigation...
The Mystery Remains Unsolved
With nobody left to contact, the case went cold. However, people that were invested in the case still keep in contact and are actively investigating to this day. Maybe someday we will discover what Mel's Hole was all about, but for now, we must wait patiently.