In this case, it is permissible for one to answer based on the edicts of his own Marja, and he does not need to give a reference of the source of the edicts or mention that there are other opinions of other scholars.
History books mentioned that the prophet (Peace be upon him and his progeny) was poisoned by a Jewish woman in the city of khaiber. His health was restored afterwards but the same illness returned and resulted to his death.
Allah knows best.
If he did not know that deliberately staying in the state of Janabah until dawn nullifies the fast, then it is valid.It is also valid if he did not know that he was in the state of Janabah until after dawn when he realized it.
