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I believe this to be Slime Mold.
It can appear suddenly in moist warm weather.
It is commonly found in mulch that contains a lot of hardwood.
It can be pink, brown, orange, tan and other colors. New hardwood mulch is the perfect feeding ground for this mold.
As the mulch ages it is less likely to support the mold.
You do not need to treat it, simply remove with a shovel and dispose of.

https://www.gardeningknowhow.com/ornamental/fungus-lichen/what-is-slime-mold-slime.htm

If you have all ready placed the seeds in the ground I would leave them for hopeful spring germination.

Do not water now.

You also can plant in the spring.

Here is a link with more information.

https://www.gardeningknowhow.com/ornamental/flowers/coneflower/growing-purple-coneflowers.htm

The leaves and flowers are edible.
The remaining of the plant is most often used to make tinctures and other medicinal methods.

https://www.gardeningknowhow.com/ornamental/flowers/coneflower/growing-purple-coneflowers.htm

Flowering will depend on the growing conditions, soil nutrients, sunlight and watering.
Here is an article that will refresh you on the care requirements.

https://www.gardeningknowhow.com/ornamental/flowers/coneflower/growing-purple-coneflowers.htm

Spread the seed over the worked soil and then compress the seed into the soil by walking on it.
For large areas you can use a lawn roller.
One tip is to mix the seeds with clean white sandbox sand (the kind the sell for sandboxes-this is non toxic) Mix the seed with the sand and then you can scatter the seed and actually see where you have sown the seed.

It is likely the plants will not have any issues with being cut down now. Dispose of the plants so that the insects and Powdery Mildew does not spread.
I myself just did the same cut back in my own garden.

https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm