What a pita eh ? I think Jon said he’s adding a resource api at some point.
You basically need to check the zip path which would be either in sublime.installed_packages() or near the executable_path()
Then it’s possible even if the zip is still there, that just one of the package assets has been overridden by a user.
The file path on the python files gets .sublime-package but things like view.settings().get(syntax|color_scheme) etc all leave you guessing.