It won't be worth the risk of another plane getting stuffed in.
I'm not sure I understand the intended context of this statement. Perhaps it's not worth the risk of renting aircraft out at all for flight training - a decision which every aircraft owner is entitled to make, without criticizm. Perhaps it's not worth the risk of allowing that instructor to send another student solo. Then control the instructor's privilages more carefully! Perhaps it's not worth the risk of sending that student solo, Then control the instructor's privilages more carefully!
Now, that said, while we're busy pinning so much responsibility on the instructor, there does come a phase late in a student pilot's progress, where for all practical purposes, they are a pilot who has yet to have a license, and they should know better. The "license" is not the line in the sand for personal responsibility. I've certainly seen a few "experienced" pilots break off a nosewheel, so it's not just students, for whom this risk exists.
But, as has been said, the flying school won't share the profits with the student when things go well, so why would the student share the losses when they don't?