I’m not sure that there is an exact answer to your question. There are so many variables. Where the tongue anatomy is removed from plays a big part. You might be able to lose pieces on the borders without much impact, but if you lost the front third and could not touch it to your pallet, making certain sounds that depend on that would be difficult. Base of tongue, where it begins to curve down your throat would be really problematic because through there pass all the nerves that give it mobility and all the blood flow which could cause the loss of the whole thing. So there likely isn’t an absolute answer to your question.

Loss of mobility through nerve loss would also compromise eating as you would not be able to manipulate food in your mouth nor easily move it from front back to your throat to swallow. These really are all academic questions. If something becomes malignant you would ultimately have to do radiation rather than lose any of what I just mentioned. Hopefully it will never come to that. Ensuring you always have a multidisciplinary consultation before it gets there will be important.