Rossian
I may be wrong but even though Delete on download was activated I still think the actual pics. could still be on the SD card.
I think a "Flag" is raised on the photo. file on the card file saying its been deleated but in practice they may be there to "Recover"
I thinks its so when you use it again it will start at Zero count.
Nothing lost nothing gained , try recovery as suggested by others, you never know it might work.
It might be that you have to put the card in a seperate "Card reader" (normally USB) and connect to your PC for recovery to work.
Not sure of this but this is what worked for me.
Cheers
OPF