Hi Neha,
I had a total glossectomy and can fully understand the difficulties in speaking and swallowing big time BUT it can be done! I just celebrated 1 year since end of treatment and can say that my speech is pretty damn good! Yes, certain consonants / sounds are harder to form or understand but compared to where I was a year ago, I've come a long way. I do have a palatal drop mouth prosthesis which helps my speech tremendously and I also saw a speech therapist weekly for about 4 months. I had a peg tube for 8 1/2 months and once it was removed I was determined to exist on more than a liquid diet if possible. Today I find that, with the help of a LOT of water, I am able to consume just about anything I set my mind to - steak, chicken, seafood, pasta, veggies, etc. - but still have trouble with bread-type foods (bagels, muffins, bread, etc.). Anyway, tell your dad to hang in there and be patient which is sometimes the hardest part of the recovery process.
Take care, Nancy