I'd say 95% is a bit too high. Maybe 30 - 50% would be more realistic, and it heavily depends on the genre. If it's an immersive game like an RPG I never listen to my own music and don't turn it off, because it ruins the immersion.
And there are also people who will listen to the ingame muaic for the first 10-20 hrs of playtime, then turn it off. I do that for some genres like TD's and sandboxes.
But I think most players will just leave it on, and will notice the absence of music as a flaw (unless it's a conscious design decision, for example in a horror game).
If you can't afford a composer (or don't want to compose music yourself), try including some CC0 royalty free tracks, it might be better than nothing.
EDIT: fuck, just noticed the age of this thread. Who necroed it? 😁