It's a dry climate and aluminum doesn't just rot. It would obviously take some money and work to bring planes out of mothballs, and probably in some cases unrepairable damage would be discovered, but I would expect most of the planes to successfully reactivate if the need was great enough. Those that couldn't be reactivated could be cannibalized for spare parts.

Consider that the Iowa class battleships spent some decades deactivated, sitting in salt water, before being reactivated several times.

They know what they're doing. But there aren't really old planes in the boneyard now. 1980s vintage and later plus a few muesum pieces that haven't been towed to the museum yet. The oddest thing out there is the tooling to make B1-B airframes.