Well, any iris that is over 100 years old will probably survive anything. I would dig a bunch up if you can, and pot them up. You can also try to just dig a bunch up, cut off any dead foliage, and dry them off, then put them in a paper bag in the garage for a month or two until it warms up, and plant them out in spring. Good luck!

I once had to transplant some irises at the end of winter while it was still cold before we motor-cultivated a part of the garden to plant potatoes.
My reasoning back then was that if I take a big enough clump of soil next to the irises and just place them in a different part of the garden the irises wouldn't even notice. They bloomed just fine and grew well until a scorching hot, dry summer. They're starting to come back up now, can't wait to see them bloom again this spring.

Good luck from me as well.

I would dig some up and plant them elsewhere and keep them warm and dry till I can plant them.

Is it possible to cover up the iris bed with a wood board or something. It can be hard to dig them all up.

Would you consider sending some over to me for postage in return?

Pebbles

I transplanted a Siberian Iris yesterday and expect it to grow without interruption. Many plants respond well when transplanted in winter. The trick is to take a large root ball so not to disturb the roots. If you can do that, I don't think the plant realizes what you have been up to.