Coffee Script is a transpiled language and it has become irrelevant when lot of the language features it offered is now natively available in ES6 and up (it has definitely inspired lot of ES6 features like fat arrow functions).
Rust on the other hand is not a thin layer on top of something like Coffee script. So it does not need to keep up with 'something' for decades. As long as it continues to do its current job of making systems programming safer and fun, it is going to be here for a long long time.
I don't think the transpilation was the issue for Coffee Script. After all, most usage of ES6 is through a transpiler anyways. Rather, I think ES6 is simply a superior language to Coffee Script. That's why it has lost marketshare. Likewise, something superior to Rust could arise, and then Rust's marketshare will be in trouble.
Rust on the other hand is not a thin layer on top of something like Coffee script. So it does not need to keep up with 'something' for decades. As long as it continues to do its current job of making systems programming safer and fun, it is going to be here for a long long time.