Happened to me on my mountain bike last year. Instinct saved me also. I rode 5 Miles home standing up or sitting on the rack.
That was the worst of it.
Most seat post are M8 x1.25 mm thread and can be replaced easily. My ME friend told me that the strongest bolt is labelled 12.9 and is rated to 175Ksi.
I don't know what those no. mean but he knows his stuff.