An interesting article by U.S.A. Today says that the future of gravel roads may be bright due to budget concerns and may benefit from the decommisioning of paved roads to gravel. The article states that several states and counties are finding that their low traffic count roads are far cheaper to maintain if they are converted from pavement to gravel.
Here in the Mid-West this doesn't seem likely now. There are a plethora of gravel roads and it would seem that in many cases here it is actually the gravel roads that are being shut down. This probably stems from the fact that there are far fewer farms now than before which means many roads are "dead roads". Roads that have no one living on them and are not necessary for access.
Sometimes these roads are left to revert back to dirt roads, or are given back into the control of land owners, who typically gate them off from public uses. It is also to be noted that recent record flooding, which took out several old county maintained bridges on rural roads, has contributed greatly to the disappearance of rural roads in the Mid-West.
Whether the mid-section of the country sees the paved roads turned into gravel is anyone's guess, but it is interesting to note that this solution is gaining a foothold with local governments strapped for operating cash.