I have managed to get my Numbers documents back:
1. I have copied the documents folder in "~/Library/Mobile Documents.delete.Sat Oct 15 09:01:32 2011/com~apple~Numbers/Documents" to "~/Library/Mobile Documents/com~apple~Numbers/Documents".
AGAIN: MAKE A COPY! Don't move the folder in case it doesn't work. Maybe even make a second copy fo the whole ".delete" folder to have a backup copy available!
2. I have renamed each document folder, removing the ending "-tef", e.g. renamed "My First Document.numbers-tef" to "My First Document.numbers". This makes the document appear in iCloud shortly afterwards. You can't open it as it is considered a document created by the Mac Numbers application.
3. I have renamed each document folder back, i.e. "My First Document.numbers" to "My First Document.numbers-tef"
4. Now iCloud seems to sync it up again and recognizes it. It reappers on my iPad and I can open it.
5. I did this for each of my 9 documents. If you have more, you may want to use a little script.
6. To get the previews back I have also copied the contents of "~/Library/Mobile Documents.delete.Sat Oct 15 09:01:32 2011/com~apple~Numbers/iWorkPreviews" to "~/Library/Mobile Documents/com~apple~Numbers/iWorkPreviews"
Now everything seems to be O.K. Documents are back. They show up on icloud.com, iPad and iPhone. I haven't done anything with Numbers the last two days thus at least for me: no loss.