the uninstall is not an arbitrary delete all files in P3D folders,
its a specific list of files; therefore third party files will remain in place,
your personal folders with your saved flights and data will remain in place,
your personal preference settings in sim will also remain as you user folder content doesn't get deleted,
your xml and cfg's there should all still be there and sim will be reading those to load again,
unless you physically remove delete these folders after you uninstall their content should all still be in place,
if you are still fe