MrP wrote a TL with exactly that POD. I don't know if it's still active, but basically, what happens is that Sophie and General Potoriek (who was riding in the fatal motorcar with the imperial couple) are both killed, and FF is seriously wounded (sustains a serious head wound) but recovers. The cumulative impact of the wound and the shattering grief of his wife's death unhinge the Archduke, though, and Hilarity Ensues.
EDIT: I found it. It's called "Pour le coeur", and though it's on hiatus, you may find it of interest: