How do I respond to the Creationists denying the existence of a vicegerent?

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This scenario can be handled by following these steps:

It uses logic (منطق) as taught in the Blessed Mahdi Howzah and a concept known as (مادة القضية) or the truth of a proposition i.e. can something exist or not exist and how likely is it?

Propositions are a vast topic in Logic (منطق) with the subject of a proposition and the type of predication being categorised in great detail.

The following three types of predication can be found in Logic: necessity (وجوب), possibility (إمكان) impossibility (امنتاع).

If someone agrees that the existence of something is not impossible e.g. the existence of a messenger or divine leader, then there are two more options: possibility or necessity.

Once they agree at the minimum, that there could be a divine leader or vicegerent on the earth, then you can ask them to directly ask the Creator, in whom they believe, to then guide them.

This puts the onus on the denier who must then believe whatever response they get, or at least still agree that a vicegerent could possibly exist. If they get a vision telling them to believe in Ahmed Al-Hasan, then his claim becomes a necessity. If they get no response, then they must continue to regard the claim of Ahmed Al-Hasan as a possibility.

Below is an illustration of such a conversation…

Denier: I believe in a Creator but I don’t believe in any divine leader / vicegerent from the Creator
Believer: did you ever receive any message from the Creator (God)
Denier: No, I didn’t receive any message from them
Believer: You didn’t receive such a message, but would you agree it is at least possible to receive a message from them?
Denier: yes, it is possible

Believer: you can ask God about who could possibly be the Messenger and await an answer

Now, the Denier will either get a response, or not get a response. Either way, they cannot take a position where they are saying the existence of a vicegerent is impossible and you tell them about Ahmed Al-Hasan