Question: What is the Islaamic ruling regarding (Ayatollah) Khomeini?

Response: Khomeini has a book in which he mentions the excellence of the Imaams (Hassan and Hussein and others) of the family of the Prophet (sal-Allaahu `alayhe wa sallam) over and above the Prophets and the Messengers (`alayhim as-salaam); (So) based upon this (statement of his) he is not a Muslim.

Shaykh al-Albaanee
al-Haawee min Fataawa ash-Shaykh al-Albaanee – Page 349

And here fatwa from Mufti  Ebrahim Desai

What is your opinion about the late Ayatollah Khomeini? Was he a Muslim or not?

Ayatollah Khomeini was not a Muslim.
and Allah Ta’ala Knows Best

Mufti Ebrahim Desai