I believe the translation of the sentence "Gott ließ uns fallen, und so stürzen wir denn auf ihn zu." is possibly inaccurate because perhaps the author translated the separable verb  "zustürzen" as the simple verb stürzen.

In my German-English dictionary:

Stürzen = "to fall" or "to crash"

Zustürzen = "rush up to"

But if Dürrenmatt was writing in a Swiss-German dialect (which I know almost nothing about other than that German-speakers sometimes have difficulty understanding Swiss German-speakers), these words could have different meanings, and I could be completely wrong.

I think a better translation would be:

God lets us fall; and so then we rush back to him.