It's my own fault really. I'd got the game fairly well advanced (though it still looks much the same - there was a status line with HPs and XPs and Gold and messages, but otherwise) - I had the monster moving and end game stuff left to do.
And I've killed it. Not quite sure how. Mucking around with bitbucket and branches I think, but suddenly pow - it had gone from the repository and the hard disk version, and there appears to be no way back - tried undelete, no luck so far.
And, of course, I hadn't done a boring old zip type back up.