Observation?

 People who can willingly euthanize their pets and put them conveniently down -- and simply replace them -- when they age or have manageable health problems that would simply slow a household's routine -- often come from families where not everybody passes naturally after a long-ish life.

Death should be hard if you're doing life right, and more and more of us human animals still value the slowed-down versions of species.  Too many people blow through life so busy winning that they don't realize what is lost. Life has so much to teach the experts.

Even an almost blind dog deserves life if the other senses are intact and he still derives joy in life. Even a limping old beast who spends her time napping deserves a simple life of familiar scents and sounds, and a quiet stroll by herself when she is able.

Don't start thinking of replacing them when you might be blessed with their presence, albeit impaired, for years still to come? If you love them, sacrifice for them. Their lives are worth it  hth.