Then someone else will force him to speak, and if he still doesn't speak hopefully someone will adapt to his communication style. Maybe you can tell him about it, but try not to emphasise how permanently you expect to be gone in that scenario. Although I suppose a three-day coma would force him to rely on someone else anyway.
I don't know if this helps, but I could never stop seeing my mother as fake after she pretended not to understand me. It might not be universal, but learning things and keeping the lessons learned forever seems to be a thing with us.
It is another reason why I could never relate to people: I couldn't catch up with the new method fast enough. By the time I had unlearned the social interaction styles I learned in kindergarden, first grade was over, and so on. Just in case you need the warning.
