Oh no Faye, I feel your pain.
If they're totally brown, they probably are gone. It could very well be that they got fried by the sun. If they feel crispy, that's probably what happened. If they're all mushy, they rotted. I think you're having the same heat wave we are and semps have to be watered very carefully in this weather to prevent rotting, especially if your soil doesn't drain quickly. I've been putting the hose on just a trickle of water and making sure only the ground gets wet - no water on the semps at all.