As a dog owner I have had 5 dogs that have now sadly passed away. As a canine behaviourist I have worked with more families than I can remember with dogs who are in the final stages of their time, and helped those families at the end. I also worked in a veterinary practice for a number of years, and there again I sat with countless animals in their final moments.
All this experience has shown me that owners do not always stay with their animal when the end comes. It is understandably an incredibly difficult time. Some owners cannot stand the pain of watching, others prefer to remember their best friend in a happier state of health.
What I can tell you, from being there at the end so many times, is that you should always be there with your dog when the time comes. If not for you, definitely for them.
Your dog may or may not be aware that the time has come, but in that moment, they are often in pain, always scared, always confused, and always sad. You need to be there for them, to reassure them in their final moments. Not only will this make the whole ordeal easier for the vet (it’s a heart-breaking moment during these times to have to wrestle your poor dog to the floor to give the injection), but your dog’s final moments will be a little more pleasurable.
Also, and for me most importantly, every single time an owner leaves the room just before a dog is put to sleep, the dog spends their last moments looking for their owner. This more often than not will bring vets and nurses to tears, and it is not how you want your dog to spend that time.
So even if you feel you can’t stomach it, you need to be there for your dog. Stroke them, tell them they are a good boy / girl, and thank them for the years of unconditional love they have given you.