“God-of-the-gaps” arguments are arguments for the existence of God that are based on some sort of gap in our knowledge of the world. The are typically derided, because historically, the gaps in God-of-the-gaps arguments have gotten filled in as scientific inquiry advances. But as Ratzsch carefully points out, if the God-of-the-gaps arguments had any evidential strength before the gap was filled in, then they have at least some evidential strength after the gap is filled in:
if something would constitute evidence of design in the context of some presumed gap in nature, then it will also constitute evidence of design even if the gap in question gets closed naturally. (p. 59)
I won’t try to reproduce Ratzsch’s argument for that claim here; I’ll just encourage you to look at the book (Nature, Design, and Science) if you’re interested. If I were to argue for this claim, I’d give a Bayesian argument — if some hypothesis can account for some piece of evidence, and is confirmed by that evidence, then introduction of another hypothesis that can also confirm the evidence doesn’t stop the evidence from providing some confirmation for the first hypothesis, even though the degree of confirmation would go down.