I am so sorry for your loss.
It is such as shock to find out at a scan when there has been no warning, I'm not surprised you feel numb. You are right, it is a very cruel trick.
It sounds as though your grief at your previous pregnancies is being brought up at this time as well, so you have an awful lot of pain to deal with at once.
(I have had several MC and found that my feelings of past losses were very raw each time, it was like losing those pregnancies again, as well as the current loss.)
It is good they are rescanning in a week, at least then you will have more clarity.
I would think about what your time limits are for things so you are clear when you see them. eg how long are you prepared to wait for things to happen naturally? When would be too long for you?
At my EPU they suggested to me to book in an ERPC for two weeks time, and if it had happened naturally by then I could cancel it, if not I could go ahead and it meant at least I knew that in two weeks it would be over, one way or another, which I found mentally helpful as I knew what I had to get through, if that makes sense.
Is there anything you can do to distract yourself for this horrid week of waiting? I find a box set of some really trashy TV I wouldn't normally let myself watch a good idea, as I can't concentrate on anything too tricky. It is also good for me to snuggle on the sofa under the duvet and have a good old cry whenever I need to. Just in case I'd also get in supplies you might need, such as heavy pads and painkillers.
for you....it is a horrible thing to have to go through. I'm thinking of you