Thanks for your question.

I suspect that your question dealt with the cut stems. I strongly suspect that this is the action of rabbits. Look closely at the cut stems. They are been severed at an angle. This is very typical of a rabbit bite. Deer tend to leave blunt ends on the stems. See:

https://www.canr.msu.edu/news/deer_and_rabbits_and_mice_oh_my

The unexpected event is that they fed on your impatiens. Generally most gardeners would say that impatiens are “rabbit resistant’. Your plants certain are evidence of an exception. Your impatiens may sprout new foliage. Time will tell. The best protection against rabbits invading your gardens is a three foot wire mesh fence. The bottom of the fence should be buried into the ground to prevent rabbits from digging under the fence. See the following for further information on these and other points:

https://www.gardenguides.com/how_8158916_prevent-rabbits-eating-impatiens.html

https://homeguides.sfgate.com/impatiens-rabbitresistant-82280.html

https://homeguides.sfgate.com/prevent-rabbits-eating-impatiens-86919.html

https://www.bunspace.com/forum/thread?tid=20966&posts_tgp_no=last

Good luck!!