What do you mean by this?
I see you as respectable for your writings and, therefore, feel that you are someone who should lead by example. That's all.
It was viable and now it's not. That means it's dead.
If you mean "dead" in regards to being significantly less viable in the current Meta, then I suppose that is the correct term to use, but considering that the word "dead" itself is, by definition, a reference to a living entity no longer living, and thus, perishing from existence... and for all intents and purposes, we'll call decks a living entity, then that is an incorrect statement. That's why I said that saying it is "dead" is a bad way to go about it. Is it no longer Meta-viable? Of course not at the moment. I agree with you 100% on that. But, that doesn't mean the deck just straight out stops becoming a deck. It doesn't mean the cards no longer exist and you simply cannot play it because it is no longer physically there. That was my point and, quite frankly, it's probably no more than a nitpick, but keep in mind that these kinds of things spread throughout the community and promote bad behaviors when it comes to deck creation, building, playing, etc. and that's not something I personally thing is good for any of us.
So, TL;DR, when it comes to the Meta, is the deck a bad idea? For now, yes. Not a doubt.
Does it mean that it's no longer playable? Well, if you can buy the cards and find a friend/local/wherever, then of course it is and, quite frankly, it's not the worst option out there.
It's possible the deck could make some kind of comeback later, but I don't see it happening this late in the season. Guardians Rising doesn't give it any new toys outside of Aqua Patch, maybe, and it doesn't help solve any of Greninja's problems, in any case.
I suppose it depends on how strong Volcanion becomes with the surge of Owl being a thing as of late. It's not like people are going to go out and sell their Greninja decks. The deck is dirt cheap and it would be a very silly idea to do so, especially when it's still a good deck in Expanded once the Meta shifts more (and it will because it always does). Aqua Patch will be interesting with it, especially with the small amount of Synergy it has with Greninja's abilities. Still, time will tell as it always has.
Regardless, I hope this clears things up.