It's always original I797.

I'm not sure whether ther is a mis-communication between you and the director of your ISO or else. US consulate always wants to see original I797, this is formal required document listed on the checklist. Before 911, if the VO is sloppy they may take I797 copy but I don't think it's the case now.

Even they took your I797 in for issuing visa, they will return to you when you get your visa back. Worst case scenario, if the I797 is lost you can still file for a replacement I797 to USCIS.

You can send your original I797 back. When your family is done, then send it back to you. Don;t worry too much about it.