1) I think the screen is connected to the camera body using a ribbon connection. Perhaps its intermittent fault is due to that connection becoming loose. I assume you would need a screwdriver to open up the casing.
2) The reliability of using adhesive to repair electrical goods may depend on exactly *what* has fractured.
Given the age of the camera and the likely high costs of repair by Sony, I would be inclined to ask the borrower for some compensation; but be aware that the resale value of that model may not be very high. Given that the damage was accidental, it may be worth considering whether in future it may be useful to take out Insurance.
However, if you feel a pugnatious solution is preferable, you could threaten to put the borrower in a bag and knock a chunk off them