Are you proposing that a strategic defeat of the U.S. would result in Sunni Moslem "piling on" and de-Persianizing Persia?
After all, the biggest oil-producing fields in Iran are concentrated in Arabistan, a majority-Arab region of southwestern Iran adjacent to the Shatt al-Arab; and that both were objects of Saddam Hussein's cupidity when he started the Iran-Iraq War.
A primordial fear of the Iranians is if the tides of war result in the Sunni jihadists ( ISIS or some derivative) take Baghdad, establish a hostile Sunni state on their border and millions of destitute Arabic speaking Shi’ite refugees pour into Iran. Iran as they say in the current vernacular, would be “transformed” and unstable. Hopefully the scenario in the Persian Gulf never happens.