That is not the case. Destructors run for things that go out of scope. When you create a reference to something ("borrowing") that reference is associated with a lifetime. This lifetime represents how long the reference is valid. A reference can never outlive the things it references (or it would be a dangling pointer), but the opposite is not true: you can create a reference with a lifetime that is shorter than the thing it references.

So basically lifetimes are used only by the borrow checker for intelligent linting. Once the borrow checker is done, the compiler loses interest in lifetimes entirely, and they don't affect codegen.