I'm not sure what you mean by "idiomatic."
According to Google Search, the definition of idiomatic that best applies is:
using, containing, or denoting expressions that are natural to a
If this is your intended meaning, I think you are asking whether in normal everyday speech a person would utter those speeches like one sentence, with only commas between the various phrases. No, I don't think so.
Let me explain. It is almost impossible to replicate spoken language exactly in writing. People have been trying for ages. Part of the problem is that every individual speaker has their own unique way of speaking. Another part of the problem is that every individual listener has their own unique way of perceiving the sounds and punctuations of sound as they are uttered. To overcome these problems, we have formalized the writing of dialogue to be as close as possible to spoken language, yet understandable without the sound of the human voice.
Where you put commas there would definitely be pauses in spoken language. Would they be periods or only commas? It depends on who is speaking and how the listener determines periods vs commas in spoken language.
The way you have written those speeches is incorrect for written language. To be easily understood in writing, you need different punctuation.
I can imagine 2 possibilities about the figure 10%, a widely
recognized rule or an intuition. I can imagine Statement A and also
Statement B. Which one is true? (I would say: Which one is correct?)
Alice is crying. There are 3 possibilities: she was fired, her
boyfriend punched her, or her boyfriend was done with her and left
her. Which one is true?
As you can see, in both examples a period needs to be placed at the end of the list of options or possibilities. "Which one is true?" is a separate sentence or question from the rest of the speech. The speech consists of three parts:
- introductory line, e.g. "there are three possibilities."
- the list of possibilities
- the question: Which is true?
"Which is true?" is neither the introductory line, nor one of the items on the list of possibilities. It has its own subject and verb; it stands alone.
Colon & M-Dash
In Example 2, the sentence "There are three possibilities" is complete in and of itself. If one were taking notes in class, it would look as follows.
There are three possibilities:
- she was fired
- her boyfriend punched her
- her boyfriend was done with her and left her
Perhaps you can see why a colon is needed; "There are three possibilities" introduces the list. It uses the present tense "are." The phrases that follows are the items in the list and use past tense: was, punched, was. (See what I did there? I used the colon, too, to set off the list. It's the way we do it.)
When writing it as dialogue, you might use the m-dash thus:
Jane said to Mary, "Alice was crying. I can think of three possibilities--maybe she got fired, or maybe her boyfriend punched her again, or maybe he was done with her and left her."
You will notice that I changed the wording a bit to make it sound more normal for concerned friends to be discussing Alice's distress. That does not affect the punctuation; it just makes for a more natural story. You will note that in this dialogue the m-dash replaces the colon. Colons are too formal for dialogue, especially informal dialogue among friends. A professor in a lecture or a lawyer in explaining one's legal options might speak with a colon in his voice, but not friends.
Is it idiomatic to state multiple explanations that way?
In my opinion, it is not okay to write it that way. If you are asking if it is okay to speak that way when in verbal communication with someone, then my answer is: Yes, that sounds okay when speaking.
Maybe I should have asked you to also explain what you mean by "idiomatic." Somehow, I thought I'd know when I looked it up in the dictionary. Now I'm not sure.