Hi there... okay what is the best chance for survival? That is the real question here...

Is this a true BOT tumor? (HPV+) If so it is said to respond very well to Chemo and radiation. So this should affect your decision. (maybe as someone here said... shrink tumor first then surgery... but that is a whole other kettle of fish as operating on radiated skin has a fairly substantial set of issues (healing etc...)Or hope it does the trick without need of surgery.

If it is not HPV+ and a standard tongue or throat tumor that has spread... then likely Surgery followed up by rads and chemo are your best options. It will be a long haul. Particularly learning to speak again etc... but it can be done.

Misskate has had a total glossectomy... in fact there are a few here I believe who have. Misskate eats, and drinks, can speak etc... Your sister's case sounds more involved, but honestly survival rate is dependent on overall health, lifestyle, treatment (who does it and how experienced they are... best chance? best hospital and drs available!) and how the patient handles things like pain and nutrition. People here who started out as T1, stage 1, have died where people that are T4, stage IV have survived.

Make the decision with your sister to do what you can for her to survive if this is what she wants. Chances are quality of life will be affected initially ( 1yr - 18 mos) but things will get better. There are many here who live on pegs all their lives, have issues with swallowing, have lost their voice boxes, have been disfigured etc. but live terrific lives. It's the glass is full theory. Life is what you make it. If she wants a life, then she's going to have to fight for it.
hugs.