In response to the OP, I don’t think option a) is even a runner in the context of the suttas.
I have doubts regarding option b) also. It does have a limited amount of direct sutta support, i.e., the adjoining suttas SN22.85 and SN22.86.
From SN22.85:
“Is it really true, Reverend Yamaka, that you have such a harmful misconception: ‘As I understand the Buddha’s teaching, a mendicant who has ended the defilements is annihilated and destroyed when their body breaks up, and doesn’t exist after death’?”
“Yes, reverend, that’s how I understand the Buddha’s teaching.”
“What do you think, Yamaka? Is form permanent or impermanent?”
“Impermanent, reverend.”
“Is feeling … perception … choices … consciousness permanent or impermanent?”
“Impermanent, reverend.”
“So you should truly see … Seeing this … They understand: ‘… there is no return to any state of existence.’
What do you think, Reverend Yamaka? Do you regard the Realized One as form?”
“No, reverend.”
“Do you regard the Realized One as feeling … perception … choices … consciousness?”
“No, reverend.”
“What do you think, Reverend Yamaka? Do you regard the Realized One as in form?”
“No, reverend.”
“Or do you regard the Realized One as distinct from form?”
“No, reverend.”
“Do you regard the Realized One as in feeling … or distinct from feeling … as in perception … or distinct from perception … as in choices … or distinct from choices … as in consciousness?”
“No, reverend.”
“Or do you regard the Realized One as distinct from consciousness?”
“No, reverend.”
“What do you think, Yamaka? Do you regard the Realized One as possessing form, feeling, perception, choices, and consciousness?”
“No, reverend.”
“What do you think, Yamaka? Do you regard the Realized One as one who is without form, feeling, perception, choices, and consciousness?”
“No, reverend.”
“In that case, Reverend Yamaka, since you don’t acknowledge the Realized One as a genuine fact in the present life, is it appropriate to declare: ‘As I understand the Buddha’s teaching, a mendicant who has ended the defilements is annihilated and destroyed when their body breaks up, and doesn’t exist after death.’?”
That does support the option b) fictitiousness of identity explanation for all this. I cannot recall any other suttas that support this explanation so directly (but perhaps there are others 
). Bhikkhu Bodhi translates some of the key terms there a little differently but with essentially the same sense, i.e., he has “when the Tathagata is not apprehended by you as real and actual here in this very life” rather than “since you don’t acknowledge the Realized One as a genuine fact in the present life”.
So I think it is a viable theory with respect to the suttas. However, one issue is that the “genuine fact” part doesn’t seem to be present in the parallels to these two suttas (we have Bhikkhu Analayo translations of their parallels SA104 and SA106 here). I neither understand Pali nor sutta Chinese so am depending completely on the translations here.
@josephzizys gathered many of the suttas that involve this particular fourfold negation (existence/non-existence of an arahant after death) in this thread:
IMO most of the other examples in that thread point in a different direction to the fictitiousness of identity explanation. I personally don’t find option b) in the OP really satisfactory as an explanation of the inapplicability of existence, non-existence, existence and non-existence, neither existence nor non-existence to an arahant. If that was the explanation, I cannot see why it would not be all over the place in the canon (I don’t buy the argument of it not being said because it would be misunderstood; maybe that might hold in some cases, but the mentioned thread does list suttas with other explanations).
However, I also have no satisfactory alternative explanation myself for the inapplicability of those 4 states if option b) is ruled out.