Welcome to Neuro Talk. I did of course read your post, and I hope some others join in. Bryanna is the best on the site for dicussion of root canals. In reality, the RC, only allows you to retain the tooth for a period of time. In the tiny canals, the infection cannot fully be contained, no matter how many times you RC the same tooth. Much misinformation comes from Dentists about this.
The only way to get rid of an infection of a tooth where it extends into the roots is to have the tooth out. That would at least get rid of one worry, and address the infection at the source.
Don't scare yourself about oral cancer. However, to get screened for this is the approiate thing to do. A thicking of the cheek, and or throat area, sore throat, should be looked at by a Good doctor, not just your dentist. Remove the worry and get it looked at.
I am not sure what kind of doctor, and I hope someone else will chime in about this. Maybe an Ear, nose, throat specialist. Your Primary Care physician may refer you to someone he knows, or look at you himself.

My father had throat and oral cancer. I know just enough about it to suggest you get this looked at. Don't get scared, we will be here for you at Neuro Talk.

If your dentist is gone for a period of time. Try to get into another one in the mean time. Be good to yourself, be calm and just go forward so you don't have to be afraid anymore. ginnie