I think C will outlive those languages, in the sense that it will exist. But it doesn't necessarily follow that your grandchildren will have to learn it. There will be some other language like JS or foobar 2050 that's just way more relevant and popular :) But they certainly COULD if they wanted to.

The question of whether a technology simply exists vs. whether it retains its popularity is an interesting one. Chairs and forks will both exist and be popular. iPhones will exist, but they won't be popular on some time scale. So it is interesting to think whether C is closer to one or the other :)