haha ok this is something I will remedy. As stated in other replies, the reason for posting here was to get feedback and improve the product (I just put to together over the weekend there)
Hello, the way that privnote deals with it is by showing a page asking "Do you want to read this note and burn it?". That will solve the issue of preview apps expiring your notes.
This is what I done! I realised this morning as I was in a McDonalds drive thru queue how easy it would be to solve just by adding an "are you sure" screen.
Amusingly, the brief contents of the note are visible in the preview along with "This note has now been permanently deleted".