How do you help a baby rabbit from death?

My dogs found a rabbits nest today, one of my dogs killed a baby rabbit (they are hunter dogs) and the other is still alive. I actually don't know/am not sure if it is alive. How do i see if the rabbit is still alive?

But i put an "x" over the nest to see if the mother will come again. What do i do if the poor thing is still alive and the mother abandons the baby rabbit?