Also they would need to adjust the refund it with inflation.
They've stolen the property. It’s not “fair” if you replace it, let alone only replace it with a lesser than value as “it was second hand”.
On the other side, a user that watched a movie 1000 times should not get less compensation.
All users are being impacted exactly the same way (loss of future access), so should be compensated the same way.
Sellers should be forced to label DRM rentals with specific time frames and penalties for violating these time periods.
The way it is done currently assumes the buyer wouldn't have bought something else that would have gained value if they knew the full terms of the sale. Instead they "purchased" an indefinite rental. Imagine if these selling practices where adopted all across the economy. It would be a mess but somehow we tolerate it because the product is digital.
Original-price refund is both simple, and (by linking the time-value of money for both parties) fair.