How does RAII works in concurrent systems ? It seems to me you need to add compile-time object lifetime evaluation (as in rust) which so far incurs a high toll on language complexity.

The exact same way it works in Rust. C++'s RAII works the same as Rust's Drop trait. The object is released when it goes out of scope, and if it's shared (e.g. Arc), it's released when the last reference to it drops.