The market forces that might be making it tempting to sell will be there either way. And with the continuing human population growth, the pile of money they can make is only going to get bigger. Another factor working against the development of a lot of base properties is that their current owners are emotionally attached to them and will make every effort to keep them, irregardless of their opportunity to graze the surrounding public land. In fact, most public lands ranchers don't rely on their livestock operation for their primary source of income. But, for the sake of argument, let's concede that if a rancher loses their federal grazing permit they will sell their base property.
Some ranches are certainly pretty but many are eyesores that resemble feed lots or junkyards.
A few new houses or condos might be an improvement, especially if the local government has some good zoning laws in place. Wildlife experts point out that it's not the aesthetics we should worry about, but the loss or fragmentation of wildlife habitat that occurs when a ranch property gets developed. This is certainly a valid concern. Once again, however, it's not a given. I've seen lots of ranches where all of the pastures on the private property around the headquarters were denuded and trampled nearly to death.