Installing Permanent Components, Files, Fonts, Registry Keys
To install a file, font, or registry key so that it is not removed when the product is uninstalled, the entire component containing the file, font, or registry key must be made permanent. To make a component permanent, set msidbComponentAttributesPermanent in the Attributes column of the Component table.
Note that the installer removes a registry key after removing the last value or subkey under the key. To prevent an empty registry key from being removed on uninstall, write a dummy value under the key you need keep, and enter + in the Name column of the Registry table.