If it's a real downpour, I'll wear Birk Eva's, Keens or Fit Flops, and change into "real" shoes once indoors. I also have some old fashion sneakers that I save for this purpose.
I learned a lesson years ago, got caught in a downpour in new shoes and it ruined them. They LOOKED fine afterwards, but the wet leather stretched with my foot sliding around in the soggy shoes, and they never fit properly again. I was sad.
That doesn't help you for a dressy event where you probably don't want to carry extra shoes though. Get dropped off at the door, and good luck!