I dimly recall this happening to me a few yrs back...

What I began doing (very sloppily) was copying the source HTML from the edit pane to an editor and saving it locally as text somewhere in my personal VCS.

IIRC, around this time, Corion suggested TiddlyWiki as a scratchpad alternative. It works well for many things, though of course little local hacks like adding nodes to your personal nodelet or public/private pads do not work.

As someone who backs up to a minimum of three local drives and also offsite, you have my sincere condolences. I know your pain.