Is the area mulched? The only problem I've ever had with squirrels is in a freshly mulched bed--they roll around in it and uproot the plants.

Put chicken wire over the plants. And yes, they'll probably be up again next year if some of the leaves are intact.

Most ephemerals have enough energy in the rhizome to take some abuse. If it keeps happening year after year, eventually they will die. I've often found that a pellet gun or a .22 works quite well on squirrels. Barring that a little dog does quite well, unless it digs as well.
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Our squirrels squash stuff too, esp. the Osterich fern and the solomon's seals/false solomon's seals.

Also, cats like to do a number of those kinds of plants too so it might not be the squirrels if it's happening at night. Outdoor cats will get in the garden and find a nice spot to roll around flattening everything. When they are in heat and a male is around, it's even WORSE.

We're also getting browse lines on all our new shrubs from the bunnies. We have a fence but they still seem to find ways in and then they graze like cattle on all my stuff. I like bunnies but I'm growing to have a grudge against them when they anhialated my new redbud bush leaving barely a leaf on it. The bark is intact but it's severely stressed. I have moved it to a location closer to the house so I can see it and will be putting construction cloth around it tonight after work. I also have to put construction cloth around my burning bushes and my witch hazel which the bunnies have stripped bare up to the top of the browse line. :o/

Barb
Ontario, CANADA

I am starting to think that my best garden helper is my lab. Her hobby is chasing deer, squirrels, and bunnys---never hurts them, but just likes to show who is boss...

LOL..mollyjenning, our lab "Clive" just passed last spring but he did get to see our woodland garden just before he died. (he's buried in it) He thought the squirrels and bunnies were playtoys and he acted like a puppy instead of a geriatric dog when he'd catch sight of them. He never harmed anything but he loved to spook all the big birds like crows and the squirrels, bunnies and cats. Unfortunately he was like a bull in a china shop so if he were still alive he'd make a worse mess of the plants than the squirrels do. We buried him under a dogwood bush with dogtoothed violets all around it and we put a bench in front of his grave so that the kids can go out and talk to him when they are feeling they need to have a private "chat". It's so cute to see them out there talking or just saying "hi".

Barb
Ontario, CANADA