First off, the fact that it works is evidence in support of it's viability. And secondly, it's not a placebo because it does work for anyone who chooses to use it.
The concept of God has other positive uses as well. There is no reason that someone using God in the manner described above should feel that if some small aspect of the unknown should become revealed to them by science, that they should suddenly then lose all trust in God. For one thing, many of the questions that we use God to help us deal with CAN'T be answered by science, and will likely never be answered for us by any method in our lifetime. And for another reason: there are many other uses to which we can and do put this God-idea, successfully. So there is no real threat to theism coming from the intellectual progress of mankind.
There have been some religious institutions that chose to view intellectual progress as a threat to their political control over people, but most religions have welcomed intellectual advancement and even encouraged it without a problem. You shouldn't allow one or two misguided instances to color the entire history of religion.
I'm not attacking you, I just stated my opinion which I thought was not at all that offensive.
That something works as a placebo doesn't mean it can't work for everyone. Unless it is revealed that it is a placebo. (And then still some people might ignore that and keep on using it.) Right now there is absolutely no evidence for (or against) a Deity, just likelihoods. I may have gone too fast for my story to make sense, I agree that a single scientific discovery won't make someone lose (or get freed from) their faith in a Deity. That would be absurd. What I meant but didn't quite say that explicitly, is that one can't take certain positions, can't simply rise above the 'two options' of faith and science and make an objective comparison. If they would there would either be many less people of faith or people who agree that their Deity is most unlikely to exist, but like the idea of it. Probably both.
Now this must seem terribly presumptuous of me, but I get that. Science, to me at least, has gained great respect. Mainly because it is not afraid to admit mistakes, and actually pursues them. Religion, on the other hand (some exceptions, of course) is predominantly conservative. A trait which simply obstructs progress - a bad thing. The great difference between the two (disregarding which thesis* is more likely to be true) is ignorance. Well, not really ignorance, not-knowing sounds better. Science doesn't know everything and has no means of comforting or giving purpose to people, like a Deity has. We have to ask ourselves, which is better: admitting that you don't know, or insisting that you're right but have no proof of it (and so might be wrong)?
*basically: On one hand there is God, with all the attributes people give It, among which (usually) the creation of this world. On the other hand, there is science, which doesn't have all the answers but does provide interesting scenarios based on actual evidence.