@Penguinsandspaniels
I agree with the others about letting DD lead the way. If you didn't mention it, would she ask to see him? If not, I wouldn't mention anything and wait for her to ask. If she does ask and it's the 'UC time of the month' I'd tell her that he was ill and not up to having company. It's not a 'real lie', is it? Alcoholism is a sickness after all.
I have to admit I'm not in a very charitable mood today when it comes to 'those men' (our DHs, exes, etc) and their drinking. So as far as your ex goes, he sees DD when it's right for her. And that determination is for you to make, not him. If it's 'his day' but you believe from speaking to him by phone that he's worse for wear or 'recovering' from a drinking bout, then he has forfeited any right to see her, no matter what he thinks or says.
And no, don't lie to him. Why should you lie? There's no need. You tell him you aren't coming because it's obvious he's been drinking. And if he says he hasn't been, well, you know the truth. So you don't argue, you simply say "I won't argue about it. We aren't coming and that's final. We'll see how you are next week". Check and mate.
@Nogoodusername
I, like you, wonder how much more Ex’s body can take. Often find myself googling it. No set answer.
I've stopped googling and pretty much stopped wondering. I guess I finally figured what's the point? It either will or won't happen in God's own good time so there's no point in me trying to figure it out.
And as I type this he's on his way once again to the ER. This time because he 'wants to stop drinking'. I've stopped speculating about that, too. He either will or won't.