OTOH, the preset info that Sonar stores, may only be able to be read by the missing plugin. Therefore, there would be no way for Sonar to know how to read that info.

Well, whatever Sonar is passing to the plugin, it would be potentially better to have that than nothing at all, I would think.
 
Bob Bone
 

This may be another case where a utility to read a cwp file and generate a document containing the project information would prove useful.

In some cases, even a fxb preset # would be enough. Shoot I'd even settle for counting presets from bank to bank to rescue a critical sound. 

Having a mass plugin replace for all instances of a missing plugin would be useful. However regarding the preset data I'm not sure what that would achieve even if you could get an fxp for each missing plugin in the project.
 
As I mentioned earlier, the chances are very slim that a newer version would read it if the vendor no longer supports the old version so what would you do with that FXP? You have no way of reading the parameter information from it and translating to the new plugin easily.

It's not necessarily to automate anything - just having something give us an idea of what the preset is might prove helpful in finding some other plugin we could use to approximate the missing plugin's preset.
 
Bob Bone
 

It would be useful to have the facility to replace a missing DXi synth with an existing VSTi version and keep the same settings.  I have lots of projects in which I have used DXi versions of DimPro, Rapture, Z3ta+, SampleTank, Miroslav and Battery 3 and most of these synths are now VSTi only.