Unfortunately rpm has nothing like a %postuntrans script, so there's no 'final' trigger for deleted packages after the %postun. What you can try is to execute the action immediately, if '%postun 0' (on final delete) was called (and no trigger has been placed by now). If the 1st arg is not 0 (upgrade), the newly installed packages %posttrans will do the job. Not perfect, but maybe better than nothing.