Should prospective cheating be reported
These students are attempting to cheat. “Prospective” is not the right word here. They have already crossed the line from just contemplating cheating to actually doing something. The fact that they derived no benefit (as far as you know, that is), while perhaps relevant to the significance of the offense and the punishment they might receive, does not change that fact. It’s clear misconduct and not at all morally grey.

To put it differently: if you saw someone attempt to rob a bank but fail, would you think you needed to report it? If you saw someone attempt to kill another person but be foiled by a lack of assistance from someone they turned to for help, would you report it? Etc.