would it still be at all possible to get published if the writer really wrote the way they spoke?
Depends. Some people speak with near-perfect grammar and sentence structure. It's how they are taught to think and speak, often from an early age. Those people would have a better chance of being published than someone who writes like Jed Clampett speaks. Unless, as we've said, the character is supposed to sound like Jed Clampett.
But two gets you twenty that any good editor will know the difference.
Or would you say it's almost 100% impossible to get their story to the public unless they either A- obtained better writing skills or B- hired a real writer?
I'd say it's about 99% impossible, because every time you make a judgement call and declare it a "rule", someone comes around to prove you wrong.
Unless the editor had some obligation to read the entire story (which rarely happens), they will probably chuck a poorly written story after a few paragraphs. If someone is serious about being a published writer, they have to learn proper grammar. Period.
Every other professional has to learn the tools of their trade, why should writers be held to a lower standard?
ETA: Posted after Sage, and we seem to be brain-sharing today.