I don't believe the Raven symbolizes death at all, but rather life, in grief of having to live after a loved one is dead. As Poe himself put it in his essay [Philosophy of Composition][1]:

> The reader begins now to regard the Raven as emblematical — but it is
> not until the very last line of the very last stanza, that the
> intention of making him emblematical of Mournful and Never-ending
> Remembrance is permitted distinctly to be seen

The phrase "mournful and never-ending remembrance" is the title of a [biography of Poe][2]. It's a theme Poe returned to several times, such as in [Annabel Lee][3].

The Raven is thus even sadder than death itself. The speaker craves forgetfulness, and will *never* have it: his heart shall be "lifted -- Nevermore". He could be content, or at least cope, with loneliness. But the Raven is a constant reminder: he lives not just with the loss but the knowledge of the loss.


  [1]: http://www.eapoe.org/works/essays/philcomp.htm
  [2]: https://www.amazon.com/Edgar-Poe-Mournful-Never-ending-Remembrance/dp/0060923318
  [3]: https://en.wikipedia.org/wiki/Annabel_Lee