Have one modal panel that renders a warning message and maybe doesn't have an OK button just a cancel button when the selected row has RI.
Make sure you reRender this panel prior to display.
Use an a4j:commandButton reRender="deletePanel" action="backingBean.preDelete" oncomplete="RichFaces.showModalPanel('deletePanel')"
or something similar to that.
The real trick is rerendering the panel prior to display.