I've heard very mixed reviews on using a puppy/new dog as the fix for a dog that is depressed over the loss of another dog in the family. We went through essentially the same thing two years ago and in asking several family friends that are veterinarians, more advised against it than for it as the puppy ends up getting all that attention that puppies do and the remaining (likely aging) dog is now playing second fiddle. We opted to let the remaining dog live out her days as our primary focus rather than having her compete with a puppy. Both are now gone so it's hard to ascertain if we made the right decision but I don't think the puppy solution is right in every situation.