Answer: Without seeing the plant, it's difficult to make an absolute diagnosis. Iris are susceptible to rhizome rot, a soft-rot that can cause the stems to collapse. I'd suggest digging the plant and inspecting the roots and rhizomes. Soft rot is easy to recognize; brown, waterlogged roots and an odor. If the plant is affected, it would be best to toss it. If you find no signs of soft rot, replant and then remove the stems at ground level. The new growth generated in the spring should be healthy and upright.
Best wishes with your irises!
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