I have got the backup installed on a subdomain now on a live server. Is that better for you? At least you got the same environment as it happened.
If that workes for you:
The steps: Actually nothing special. No updating, no changes in the config or something. Just playing with styling on of the textblocks on the homepage.
When hitting "save", the page frooze. No response at all. After 2 minutes I refreshed the page and whole page was gone. Only the menu was there. In the whole system the SPPB created page was gone, in backend and frontend. Like it was never there. All I can say. Really nothing to be found, except the custom saved addons and saved rows. Those were not lost.
Worked for about a day without making a backup, thought I would do that next.. unfortunaly too late.
In short, I did nothing more then some styling some addons in the frontend.
Hope you can find some what could have caused it, a crash, freeze or bad server response can always happen. But the saved work should not be vanished.