I've never had any problems with it surviving. The first year I put straw over the top after cutting it back. The next year, when I cut it back I just let all the cuttings fall on top of the corms and let that be the mulch. That also worked fine, then you just rake it off in the spring.It not only survives in zone 5a-5b, it multiplies. I now have clumps of corms.
Cheryl

Mine survive well too! Some years I don't have time to cut them back and the leaves do serve as some weed control too.
I've noticed they don't multiply as quickly if I cut them all...I'd say, its one flower its ok to "ignore" for the winter!

Let us know...
Wendy