What could be changed for the future would be that you are able to still see/download the note private key after depositing if you still have the tab open like in this case.
So basically the question is: should we refund if the user only has the guarantee letter but not the private key, or should we stick to the rule that if you lose the private key you lose access to your funds?
I would personally believe this user and make the changes mentioned above to prevent something like this from happening again. At that point it would be only the users fault if he doesn't save the private key.
Currently the private key is generated by the user in the frontend on the main page. If we were to show it on the next page as well that would imply we generate it ourselves and store it, that's why we didn't do it.
So this raises another question for the community: Do you think we should show the private key on the deposit page as well if that implies we also have access to it?