The answer is not simple and not the same for every situation or point in time. I definitely think it is a good idea to give your loved one a chance to talk about what is happening and how they feel about it. However, not every person is going to want to discuss this. Many of them may try to hide or deny their memory loss. In fact, it would not be uncommon for someone to get angry if you brought the subject up, especially if they are in the middle stages of Alzheimer's. I'm not sure it is useful to let the person know what they will face. If they ask about this, you can share it, but I think it can be very discouraging and might even make the person very depressed. I think the message I would give is that you will help them at any stage along the way and that you will work together with the doctors to help them find the best ways to remember things. Finally, it is important to assure them that you will always love them and think the best of them, even when they can't remember something.