If the student followed the checklist correctly there wouldn't have been a problem....what better learning point? bet they won't do that again....but I don't mean to be flippant and thank god no-one was hurt!
or....don't ever let them do anything alone until they have passed the PPL test and never ever let them go solo as they might make a mistake! Obviously there is a balance and they have to learn, had the student had sufficient training to start alone....obviously had if already gone solo.
As to the drival about never getting in or out of an aircraft with the engine running......
no...I'm not going to bother responding!
As to the original point regarding the insurance tell them to shove it.....that's why we have insurance because accidents happen...as long as we learn the lessons from the mistakes..pref' someone elses!