I have a Canon S400 camera and I NEVER connect the camera to the computer to get the pictures off it. I have a $12 flash card reader that mounts and acts like a CD drive. I can pick and choose the images I want to copy to my hard drive.
Using a flash card reader, the only way to get images to delete from the card, is to drag them to the trash and then EMPTY the trash. If I drag images to the trash and don't empty the trash, the images seem to be gone from the card when I unmount it and put it back in the camera, and when I look in the trash, I don't see them there, but like magic, when I mount the card again, there they are - back in the trash!
I don't use iPhoto - found it slow and clunky - so I don't know what happens when you use it to delete photos from your camera, but I wonder if just buying or borrowing a flash card reader and mounting the flash card and looking in the trash (assuming you haven't yet emptied it) might reveal all your photos there. Worth a try!
If you're lucky enough to find your photos in the trash, just drag them out of the trash unto the desktop or into a folder and then you can get them from there into iPhoto if you want to.
Take care, Margaret