I lost Bob and Sam three weeks apart this year after having them both for over 14 years. It was just heartbreaking and has been the most difficult thing I have ever gone thru. I don't have a family so they were my family and I still greive for them.
But life goes on and I tell you the best thing I did was to get another dog. I rescued a dog that surely would have been put down and it is a wonderful animal. I can't think of a more fitting memorial to Bob and Sam then to save another dog in their memory. I believe they would like that.
Try to prepare your friend and be sure to get plenty of pictures for they will comfort your friend later on. Sometimes the best thing we can do for the animals we love is to say good bye even though it may be the hardest choice. Remember all the great times you and your friend had with the dog and I promise it will bring a smile to you.
So, your friend may well have to say goodbye and it will hurt and be sad but after a period of time get another dog then everyone wins.
Good Luck