I'm sorry, I must admit to not being able to answer your question, except to say "it's not possible to answer your question".
First, there is no formal definition of martial arts. In my book, MA involves M-16's, throwing hand grenades, driving tanks, and battlefield management - not self defense. But others don gloves and get in a roped-off ring; or don a singlet and go mano-a-mano without hitting the other guy, or maybe get onto a mat and only kick the other guy - and they all call it "martial arts".
There are those who take one- or two-day women's self-defense classes offered by a church and are given a myriad of lifestyle changes they can do to mitigate becoming a victim.
There are those who "say" they know a martial art and are complete charlatans.
There are those who "knew" a martial art, but gave it up decades ago.
There are those who are linebackers or bodybuilders and have the physique alone which can make potential perpetrators think about another mark.
A runner might be able to outrun an attacker.
An untrained mother defending her children is an absolutely formidable opponent to tangle with.
A Medieval Times performer deft with a lance, sword, and mace could make mincemeat out of a perpetrator with a rake handle, a baseball bat, or a length of chain (and who, in my opinion, are more of a martial artist than anyone in a dojo, dojang, kwoon, or gym even though their martial arts study is limited to historical context).
What about someone only trained to use a rifle or handgun?
What about someone who is an expert in ancient medieval or feudal-era weaponry?
What about any common soldier or officer?
What about any police officer?
All of these kinds of people (except the mother) have been trained in some way to deal with adversarial antagonists. The definition of martial arts is so overly broad that each of these groups of people, by someone's definition, are considered a "martial artist".
Along a different vein, much of what the self-defense community teaches is avoidance and managing lifestyle changes - that is often more important than managing a situation in which all of that is ignored or couldn't be avoided which necessitates a physical response. And here, how can you know you avoided a situation just because you took that advice?
My point is that every term in your question is so broadly defined and subjective, it is not possible to answer it: "suppose", "you", "know", "martial art", "how likely", "get a chance to use it", and "self defense" all mean different things to different people.