A good software engineer should be able to learn a new language in a week or so. If there is something inherent in the language which makes this not possible, e.g. pointers, generics, functional v. procedural, etc., then the software engineer has a gaping hole in his/her knowledge and may need some additional training.
That point aside, I think the discussion here makes the decision C, mostly because of unknown future support for Rust--it is too new to know.
Unless C has an easily describable deficiency which will be covered by a different language, there is no argument here.
An engineer not being willing/able to learn C does not count as a deficiency in C. The same is true for Rust.
Also, if one particular engineer has a strong preference for Rust, for the preference to be an informed decision, the engineer must already be familiar with C, so there should be no problem for that engineer to work in C if the decision goes that way.