if I cut them all the way down will they come back They look terrible
Impatiens. There are several varieties, but one you see everywhere. You can probably pinch them all back. You may want to look it up on plant care sites (with the correct spelling).
I'm guessing yours have gotten too high and scraggly looking and you want them back closer to the ground and growing fuller, rather than up. Most people get impatiens for their ground-cover tendencies. They can be pinched regularly and long before they get scraggly.
Go ahead and pinch that growth back to say 3 inches high and the remaining stems should sprout. Its probably a good time right now. Go for it. All that energy that was going up those long stems should make fresh new growth like crazy. If you want, try to root your cuttings in water in the house and replant them or give them to a friend or neighbor.
Gardening is great. Gratifying and meditative. Love it.
Cut them back, give them shade, and lots of water. You'll be rewarded again soon!
I'm pretty sure they don't come back.