I honestly agree with every single person -- but for *me* the answer has been different with every single dog.
There are some dogs who just have such a force of "will" that they are NOT going to be stopped. Otehrs? if they are miserable the way they are that tells the story.
I don't mean this to sound anthropomorphic but maybe it will help. If this dog COULD talk, and you sat down with them to share a fresh bowl of water -- what would they TELL you.
Little Miss Kee Shu never EVER "gave up" in her life. She was a survivor to the max -- she was always gonna move *forward* (even if she couldn't remember where the heck she was going!!)
She got SO elderly. Couldn't locomote at all without falling over. But she was gonna EAT. She enjoyed her naps. She enjoyed being WITH. No problemo.
I wanted her to just 'Pass' -- she was SO ... "elderly" is the only word for it. David and I argued for two months about it. But it was easy to keep "going" because -- much as I hate to admit it -- she just kept going (think "Energizer Bunny" in 2018 on the same baqtteries??)
But lo and behold -- one day she just plain STOPPED eating. Then it got easy. That was the que we'd waited for and she DID give it to us. Suddenly, nope -- would *like* to want to but nope can't eat.
That night we let her go in perfect peace.
My Foxy - the last "infection" he had was really his body just plain shutting down on him (he was 18) - but HE wasn't done. NO way. He wanted to eat, he wanted to TRY to walk, he wanted to TRY to pee on his won. His will was VERY strong -- and he'd always made himself abundantly clear to me.
I gave him a few days ... and finally that last morning Nope ... DONE. He may as well have screamed it at me. REfused to stand. I gave him water by syringe -- he SPIT it at me.
Ok ... I get it I get it. I took him straight up to Dr. Bailey!
Ms. Socks had cancer -- she had a sudden painful "burst" where a nodule ruptured and she came in ... looked at her food bowl, turned around to me -- looked at her bowl again, SIGHED HUGE and turned around and very **deliberately** walked away.
Done.
All 3 very very different dogs. All three "quit" at different places. But all 3 made it abundantly clear THEY were done.
For **me** that's more comfortable. But you have to be really comfortable making that sort of judgement about what the dog is telling you.
All I can say is think of THIS dog's personality. How would THIS dog feel about not being continent. Some dogs are beyond fastidious. If Billy had ever soiled himself he would have been so beyond miserable it would have plunged him to depression.
Kee Shu? No biggie to her.
Does that make sense?
I think it also has to be what is in YOUR confort zone. If you've always had a really active, athletic relationship with this dog, and if Elderly or frail types of behaviors are uncomfotable for you, then I don't think it's wrong to consider that warning enough.
This is such an incredibly personal thing ... compounded by the unique relationship each of us has with each dog -- there are no wrong answers here.
Personally -- I give HUGE HUGE HUGE merit to what Jackie said -- I'd rather let go a day too early than a day too late.
The last "story" I'll leave you with was my original heart dog Prissy. Pom/peke mix - she lived to be 20. She went thru all the abuse wtih my ex-husband and all the 'bad days'. I was so bonded to her it was literally unhealthy.
At the end she had a series of strokes. Not only was I not mentally able to even *think* of euthanasia (I am NOT proud of how weak I was at this point) but my ex and I were literally half an inch from living on the street -- and I honestly didn't even have the GAS to get her to the vet to beg them to euthanize her and let me pay later.
I put her thru h#ll that last day. I allowed her to see me in full grief -- I simply sat and rocked her all day long just waiting for her to die.
She wouldn't leave ME. (another dog with a huge life-force and self-will)
Finally the phone rang and I left her on the sofa so I didn't disturb her while going to answer it. She "left" while I was 15 seconds at the phone.
I'm not proud of that -- I will NEVER EVER allow that to occur with another dog.
My point is this -- don't just examine the dog -- examine yourself. The dog **must** be first. If the signs are there that this dog is "done" -- so be it. Gather yourself together and don't let them see you fall apart.
And sometimes YOUR mental state may be the biggest part of "when" -- because the more frail they get, the more labored it all becomes -- the HARDER it gets to let go.
Tiffy said "Quality of life" -- I'm going to add "dignity" to that. Whatever THIS dog considers "dignity".
For every single dog I've ever owned -- that word "dignity" really did mean something different to each. But it also has to mean something to you.
Either this was helpful or it was totally "not". But it's a tough thing to put into words.