Your linguistics is sound, but your insistence of identifying the Mohammedan Allah with the moon god of the pagan Arabs is flawed. Al-ilah has the same significance in Arabic as ‘o theos in Greek, the definite article having the same force as the capitalization in English, of indicating the one existing deity of a monotheistic religion. Arabic speaking Christians refer to the All-Holy Trinity with the word Allah when speaking Arabic, but, denying the Mohammedan conceit that the Arabic word for God is the proper name of the one existing deity, switch to God in English, Dieu in French, and so forth.
It is only if one accepts the Mohammedan conceit that Inshallah means “If Allah wills it”. As an Orthodox Christian, I reject that conceit. The correct translation is “If God wills (it)”. The phrase is used by Arabic speaking Christians in exactly the same contexts in which English speakers would say “God willing”. I even knew an old Orthodox Christian woman whose name was Inshallah — her mother hand been thought barren and had taken to answering questions about when she would have children with “Inshallah”.
Can Gomez Addams please come and get his butler Lurch back where he belongs.