I haven't been in your shoes, either - I can't imagine what I would do. I have a friend whose son went to prison and she is now her gk's mother in her mid-60s. She seemed to have figured something out because she is out among the living and involved in things that interest her. She is a very strong person.
You offered yourself some advice that makes sense to me - to take some time to be alone to really grieve this for as long as it takes. Then you can start finding your way back. My only advice is to be sure to take care of yourself physically while you're going through this - getting outside and walking around, looking at things and breathing fresh air at least is an old-fashioned therapy that has some benefits. Good luck with this.