Doesn't look like there was much holding that terminal on in the first place. If the cell can't be warrantied, maybe a pop-rivet would offer a solution. Replace the rivet's shaft (which is designed to break away) with a finishing nail or something else that would swell the rivet but not break off. Taking it a step further, you could scuff up the nail with sandpaper first and tin it with solder. That way soldering on a new terminal of some sort afterwards would be easier. I don't know if solder will stick to steel though. Another option would be to use a copper or brass rod for the nail. With a power drill and a file you could form the shape needed to set the rivet. That would hold the solder if the nail won't.