Probable reason for teeth extraction could be that post your mother's first radiotherapy, she may be having limited mouth opening (trismus) and glossectomy is a open mouth procedure and it may be difficult to reach the tongue in current setting. Second reason could be that they are also planning re-radiation and the teeth that are already in bad shape may not be able to survive another onslaught.

Sandy is right about second opinion from oncology dentist as a normal dentist may not be able to assess it correctly in light of previous treatment and planned treatment.

What is the outcome on having wedge biopsy? Is your mom's onco ok about it? Has your father been able to get the details of treatment that is being planned?

And yes, you can read about Miss Kate here: http://www.ucsfhealth.org/patients/brown_kate/index.html

This should answer few of your queries.