Sorry to hear OP. I will post and then unfollow as I find it so hard thinking of losing my 16yo boy who went this year. Like you, he was deaf, poor sighted, bit incontinent, needed hand feeding etc for quite a while towards the end. At about 14 he had something that looked exactly like a stroke in the night - I was convinced we were losing him - took him to the vet as soon as it opened and turned out it was just an inner ear thing that a lot of the oldies have and it looks terrifying but isn't so bad. So don't panic with things like balance/circling furniture, he's an oldie and they have good weeks and bad weeks.
With respect, fuck the carpet, it's a carpet and like you said it's ruined now anyway. Likewise we had a kind of sacrificial rug for the last 6m or so in the front room, was cheap and got pissed on / vanished etc a lot , and we threw it away once he'd passed.
He loves being part of your family and that is the main thing. I agree that "you'll know" when the time is right for him. It's our job to love and care for them until then.
My boy went on for a very long time months after we thought "surely he's going to pass tonight" but he was such a fighter, and he absolutely loved us, he would never have wanted to go "a day too soon" and that is why he kept going. We gave him a lot of painkillers and sleeping pills from the vet to help him in those last weeks, half expecting he'd pass over, and he could have given up sooner with all of that, but he never did. I so hoped he'd go on his own terms but ultimately we had to PTS as his pain and weight loss was severe and stopped being helped by the medication and the balance had tipped from manageable for him to unfair. Hardest day of my life and I have never stopped mourning his loss. Even then, we made the most of every day - the day before PTS I gave him his sleepy meds and carried him around town to all his favourite places, he managed to eat a sausage (!), and he loved it.
No one knows your dog better than you. I can only say having been through those very uncertain late stages where you can feel like today might be the day they go and the. they go one for months and make tons of wonderful new memories - give him every chance. You will be amazed at how resilient they are and you'll know when the time is right when there's absolutely no doubt at all left in your mind (and his eyes) about it. That moment does come and you'll know when it does. Don't underestimate how hard it is to lose them and make the very most of every precious day together you have. xx