Peter Molyneux forgot whom? The God.
Nope. "Who" in the headline is used as a relative pronoun, which is considered correct even when it is the object of the relative clause.
Who can act as the subject or the object of the relative clause:
The woman *who* I saw yesterday was Sheila.
(who refers to the woman and is the object of saw in the relative clause)
(I'd argue "The God that Peter Molyneux Forgot" would sound more natural, though..)