employer submittance of paperwork

I had a question about paperwork. So my boss filled out his sponsorship paperwork and submitted it about a month ago. He put a cover letter on it request speedy processing because of my circumstances
My visa ends December 20th obviously that is coming up quickly.
I have heard through looking through here that I am allowed to stay up to 28 days passed my visa correct? but I am not allowed to work? This is fine, however is there anyway I could apply for a small extension even like 30 days on my visa to wait for his to come back? I am getting very nervous about this.

While I do have money to support myself for another month without pay. I would prefer not to do that along with what if it doesn't come within the 28 days. Him and I are just out of luck and we both part ways? how does that work?
Thanks for any advice

Also if anyone could link me to the 28 days after my visa expiring that would be great. I have been trying to find that on the UK website and am not able to locate that.