Language is definitely the most self-important part of the mind, and the only part proclaiming itself as "indispensable". The voice in our heads is most definitely telling us "if I wasn't here saying these things you'd be dead by now."

The math part of your brain never shouts equations at you to guilt and cow you into submission to do things you otherwise wouldn't or forego opportunities to quell the demons within. We also never consider that losing another faculty would "completely stop our ability to function", but we do think that about language. This article proves otherwise (its just another function, like math or the ability to do spatial reasoning).