Liz,
I understand your anxiety about the situation and would not wish these circumstances on my worst enemy. First, have a big hug an take a breath.
I'm not overly enthusiastic about the way this was handled by this dentist. If he performed a full examination and oral cancer screening he should have made you aware of the condition of your mouth and oral cavity and any and all conditions and/or concerns he had as a result of his examinations prior to commencing any treatment. In Canada we have many different types of examinations and a specific code for each. If, in fact a complete examination and oral cancer examination were performed then i have an issue. If he only performed a specific or emegency exam ( these are done to address the immedite problem and do not include evaluation and or comment about the patient's whole mouth. Remember, I am speaking about Canada and the regulations under which I practice.
I assume that from your above post that you did in fact recieve a comprehensive exam and oral cancer screening. In Canada it is required to inform the patient about all abnormal findings, possible outcomes and treatment options that are available as well as outlining the treatment that I would suggest. This is informed consent.
To call a patient after the fact and be dishonest about the reason that they need to return is not only unprofessional, but unethical.
I hate to say this about a colleague, but he messed up. You have options and avenues you can pursue if you want to deal with this issue.

It is not abnormal for the gumes to become hyperkeratotic if teeth are not present and not replaced. Eating pushes food onto the gum tissue and causes the hyperkeratosis, similar to callouses forming on the hands due to repeated trauma. This is the bodies way of protecting the underlying tissues.
This dentist told you that the area looked sore...was it or has it every been sore?
Did he explain why he felt it could be serious and why an urgent biopsy was required?
All of the mishandling aside,I think you should have the biopsy just to ease your mind.
I know you don't want to go down the path that would be before if this is something bad. I do know however that if you have to that you are strong enough to do it and that you will for your families sake. You are a strong woman and an inspiration to many of us here. I'm here if you need me.
I'm sending you my personal e-mail address and phone numbers if you want to talk. Call me anytime.
You are in my thoughs and prayers Liz.

Mike