I've encountered this problem a few times, a page will go missing from the Umbraco content tree but it will still display on the front end.
It doesn’t show up in the recycle bin but you can find it when you search for it by name, and when you try and open it you get the following server error:
“No Document exists with Version 'xxxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxxx”
It turns out to be due to data being orphaned when the database is updating, you can find out more here .
I followed the advice on the Umbraco issue tracker and deleted the last entry for the affected node in the cmsContentVersion table, it worked for me.