I like some of these ideas to help save the day...
This is a cute see-through option, I love that you can see the raindrops on this.
What an adorable umbrella, maybe you could do this for the bride and groom? Cute.
A little different but very Victorian. I like.
This is so sweet, best thing is it's 100% waterproof (I think I'd like it in ivory more)
All umbrellas from Umbrella Heaven
I love the idea of having your photo's indoors regardless, you can get some awesome shots as you can play with the lighting. I'm thinking, at our favourite bar/pub and cafe. A beautiful friend of mine had hers at her Nonno's deli, the pics looked amazing.
What were/are your plan B's?