As long as they were planted at the proper depth to begin with, they should be just fine. Any mulch, leaf fall, etc. that might have been added by you or allowed to remain from the Nature of things, would be added insulation. I don't have Dahlias (geesh, that spelling looks wonky!) here, but I do have Glads and they've always done just fine for me in respect to returning. You might consider carefully digging and lifting them though - on a warm day - to inspect them and divide if there's anything there ready to be divided (not sure how mature they are or how long you've had them). If you do decide to dig/lift them - as long as they aren't mush or unidentifiable from other organic matter in the ground, and are more or less firm - they should be fine. Wouldn't hurt to lift them and if found to be healthy, to cultivate their sites a bit, turn the soil some, & add some bone meal when re-planting them, or any other soil amendments that you find worthwhile at the time (notably if the soil has become very compact).

I'm in Knoxville & I have glads & Dahlias that have been in the ground for 7 or 8 years (hate to admit that!) and they keep coming back every year !

Thanks so much for the quick responses. Am so excited that I should have no problem. Will take your advice and take a peek and amend the soil.