He's feeling so much better today! He still walks on three legs most of the time, but is using his foot to balance and is starting to use it to walk, too! I am so relieved!!!
We went back to the vet's this afternoon; he was happy with the way things are going. So now we have to keep the paw as clean as possible (flushing out with boiled, cooled water after each walk), and continuing with the antibiotics.
They never found what caused the infection, and this is apparently the danger - once the antibiotics are finished, if there is still a foreign body in there, the infection may flare up again, which would require more investigative surgery... But right now I am just thrilled he is feeling better and back on four feet again.
I haven't used the cone on him; he's been sleeping next to our bed so we can hear if there is any slurping or licking. Naturally, we are a little tired....