You know that's incredibly pedantic. It is still a period in which you can't die. It's holmgang with extra steps.
There is nothing "pedantic" about it. Until Walking Dead is triggered, you're still taking damage just as normal. No "invuln" is actually taking place until your HP actually drops to zero. Until that happens, Living Dead is doing absolutely nothing. Same thing with Holmgang too.

I get you want to try to show some support for what is clearly the worst tank "invuln" skill and I don't care if people do that, but please don't try to outright lie about it and proclaim it's "20 seconds" of invulnerability. That's just blatant Never Needs Sharpening going on.