bytheway asks:

“Specifically, wouldn't the effects of sublimation erode away the craters?”

Inside the orbit of Saturn, you betcha. But for ‘pristine’ comets (by which I mean, have never been kicked into the inner system), then no. Out in the Kuiper belt and Oort cloud it is so cold and distant from the Sun that sublimation would become a negligible mechanism for erosion.

http://www.harmsy.freeuk.com/oimages/oort_cloud.jpg