The promise at Nepenthe is simple: they will erase the memories you cannot live with.
After the procedure, psychologist Noor will assess you for two things: your mental wellbeing, and the successful erasure of the memory. But there is no assessment if you choose to delete the memory of the Nepenthe procedure itself. If you do that, you're on your own.
And what if one day, out of the blue, your memory is offered back to you - would you want to remember what you've chosen to forget?