Thank you for showing such understanding of the bond your friend had for his companion animal – he is lucky to have you as a carer. It would be ill-advised for him to take on the commitment of a puppy or any dog that is not already well-trained. This in itself would tend to make adoption the more likely option since not many well-behaved adult dogs are sold (as understandably most dogs sold by their owners are being sold as a last resort).

Can you imagine the companionship that your friend can reciprocate to a rescued older dog from a rescue shelter? Perhaps there is an older dog who has been rescued because their owner has recently died of old age – and these dogs are normally not a popular choice for adoption with families. I think this is a lovely chance for both your friend and his potential adoptee to share some much-needed companionship in their later years.

P.S. Most shelters need evidence that their animals are going to a suitable home – so you may need to help make it clear that you are partly responsible for the well-being of the animal being rescued.