Absolutely you can keep all the iris's that can be rescued. Especially if you only have one rhizome left. Save all you can.
I once was gifted an iris from a friend who I know had the iris borer. And she cleaned it up nicely. I didn't get it planted right away. And thankfully I didn't. When I got around to planting it I noticed little bit of what looked like wood shavings laying under the rhizome. And sure enough, there the little bugger was inside it yet.
I generally have more than I want to keep. Even when I have to thin out some beds I will throw out the small ones because I just cannot plant them all. I have given away, literally, hundreds of rhizomes.