> Would it be more accurate to say that Rust guarantees the droppability of owned values?

I'm not really sure, exactly, since "droppability" isn't really a thing that's talked about, because as you're sort of getting at here, it's universal, and therefore not really an interesting concept.

> I know there's a guarantee that &'static items never have their underlying value dropped,

Even this is sort of... not correct. Consider this program:

  #[derive(Debug)]
  struct Boom;
  
  impl Drop for Boom {
      fn drop(&mut self) {
          println!("BOOM");
      }
  }
  
  use std::mem;
  
  static mut FOO: Boom = Boom;
  
  fn main() {
      let mut s = Boom;
      
      unsafe {
          dbg!(&FOO);
      
          mem::swap(&mut FOO, &mut s);
      
          dbg!(&FOO);
      }
      
  }

This will print BOOM, as the initial Boom is swapped out from behind the reference and then dropped.