[stmt.return.coroutine] p3 states:

If p.return_­void() is a valid expression, flowing off the end of a coroutine's function-body is equivalent to a co_­return with no operand; otherwise flowing off the end of a coroutine's function-body results in undefined behavior.

which the bolded function-bodys refer to? Since [dcl.fct.def.coroutine] p5 states that

A coroutine behaves as if its function-body were replaced by...

If we argue that the replace function-body is just notional(i.e., the replacement process is not actually happened), I would say the expound in [dcl.fct.def.coroutine] p11 is anyway based on the replaced one.

The coroutine state is destroyed when control flows off the end of the coroutine or the destroy member function ([coroutine.handle.resumption]) of a coroutine handle ([coroutine.handle]) that refers to the coroutine is invoked.

Presumably, the end of the coroutine refers to the portion after co_await promise.final_suspend() ; in the replaced one. Maybe, there is room for improvement for the above provision in order to eliminate the ambiguity.