Earlier I said, heck with it, and lifted my dahlias (stargazer)

Then two nights ago it froze hard (-8 C -- 20F)

Then I remembered another bed of dahlias.

I lifted them too. Ground wasn't frozen.

Is there anyway to tell if I killed them?

Also:

Do I need to divide? What do I get if I store and plant the whole root?

Is dividing in spring an option?

Spring division is an option and easier to see eyes poking out. If you plant the whole clump you'll have many stalks, a bushier plant that is more difficult to support but with more flowers and tubers that keep right on reproducing underground making division even tougher as each year passes. Over time the flowers become weaker and fewer. It's really not that hard to divide every year or two. After that, it gets more challenging as the clump grows and tightens.

You can see examples of 1,2, and 5 yr clumps at the link below. Also photos identifying eyes and approximations on where to divide into single tubers. Practice, practice, practice makes it easy in no time at all.

I ended up with a bumper crop. 3 milk crates of good sized tubers from a single packet of seed.