Yes, the stem rots off at the base when the soil is too wet. They are particularly prone when they are weakened from other problems like mites. Make sure you use fresh soil to plant them and make sure they aren't overwatered. Regular bedding Impatiens can recover very well from wilting occasionally if they run short of water, so don't be too eager to drown them every day.

A good way to plant impatiens in hanging baskets will be to use watering crystals ("soil moist, etc") to retain moisture. This will not lead to root disease, and you can water less often.

Good luck.