I can definitely see how paper towels could be better, but I couldn't switch mine given how much they burrow in it. It's practically their staple activity.
As for dying from substrate ingestion, if it was fed outside the tank, and the snake just casually ingested aspen, then pardon me for the "coldness", but that thing deserved to go. I can understand killing mice because not all CB snakes can subdue live prey, but a snake that casually eats substrate and dies is not a "fit" snake. In keeping some sort of natural selection, that snake was definitely slated for "untimely demise". The average snake, for the original poster's information (Fritz), can live on aspen at the very least, and with minimal supervision they can eat on it too. Papertowels are much easier in terms of price, and in keeping tight control on environmental conditions, and for inspecting health aspects.
Despite claims otherwise, I think that as a wild animal, expecting a helthy snake to be able to eat on substrate is not an outrageous expectation.
I do realize where you're coming from, Amanda, and I must admit that if I knew the person whose snake died that way, and I knew that snake, I might be compelled to switch to paper towels myself.