Really? Where I live a patient is always able to refuse any medical procedure or treatment, unless they’re unconscious or otherwise mentally unable and the procedure is considered necessary to save their life. They certainly can opt for a non-ambulance transfer, though here it would be free even though a regular ambulance service typically isn’t.

Consent for treatment is a core principle of medical practice.

I think the idea is that if it's mandated, then the ambulance should be covered by some kind of insurance since it was medically necessary and not just Ol' Bob, the hypochondriac, calling because his tin foil hat fell off.

Except that's not how it works. Ambulances are almost always out-of-network, so subject to MUCH higher OOP expenses. It's spelled out in the article.

And what would they do if you refuse?

Who is "they" in your question?