My impatiens' leaves start to turn a lighter green, then they start to look sparse, then they begin dying. All the flowers and leaves fall off the stems. All that is left are the stems. I spoke with the greenhouse I purchaed the flats from, and they were not much help at all. I've planted for several years, and never had this problem. The plants have always been full, like a bush of flowers. All of the flats have done the same thing. Plants were placed in different areas.
This article will help with pinpointing the likely cause of the plants’ demise: https://www.gardeningknowhow.com/ornamental/flowers/impatiens/impatiens-problems.htm
Just in case you cannot save them, you may want to take some cuttings (provided you still have some healthy foliage). They propagate easily and this way you can continue to enjoy them. This article will help: https://www.gardeningknowhow.com/ornamental/flowers/impatiens/impatiens-rooting.htm