Iris are amazing. I would plant them. I tossed what I thought were old used up mothers in my compost pile and they spouted some more babies. If you toss them toss them into your flower beds. If they don't make it they will decompose and if they do you have another iris.

Chere

What is a "small amount of rhizome"? Did you cut across the rhizome with a cutters or something? If not, if you have most of the rhizome then there is a good chance it will grow.

When we dig and divide irises, most of us trim the roots a lot, and trim the leaves, so it is the rhizome that is left and is what will start a new plant.