軽く調べてみた。

> 14882:2003 15.1/4
>The memory for the temporary copy of the exception being thrown is allocated in an unspecified way,
>except as noted in 3.7.3.1. The temporary persists as long as there is a handler being executed for that
>exception. In particular, if a handler exits by executing a throw; statement, that passes control to another
>handler for the same exception, so the temporary remains. When the last handler being executed for the
>exception exits by any means other than throw; the temporary object is destroyed and the implementation
>may deallocate the memory for the temporary object; any such deallocation is done in an unspecified way.
>The destruction occurs immediately after the destruction of the object declared in the exception-declaration
>in the handler.
最後の handler が処理されるまでは例外オブジェクトは破棄されないってことらしい。

>551
例外オブジェクトの型は最上位の cv qualifier はずした型になるって 15.1/3 で書いてある。