Hi Lori- hope you find your snake. My ball python got out in the reptile room one time, I found him across the isle on the very top shelf of aquariums(6 feet high)- so in other words, dont forget to look up in your searches.
Up high in a decently warm, dark closet is where I would go if I were a ball.

My ball was given to me by a school teacher, who had it go missing in a school for several weeks till a janitor found it.
I dont trust any petstore-type add-on screen lids farther than I can see them (other than sliding top ones that are built on). Too often they just dont fit securely enough, or even if clips are installed, they might be able to flex in a spot. I had a 3 foot cal king escape through one that was "properly installed".
When in doubt- extra bricks and encyclopedias do well. lift at the lids at every inch of the perimeter and make sure there are no spots that can be lifted reasonably easy.

I have never heard of one ball eating another, but anythings possible, though I would think the other snake would be obviously very fat.

As Shannon said, make darn sure its not just wedged tightly inside some piece of decor in the cage, or elsewhere in the cage.

Let the house go nice and dark and quiet at night, and then look around with a flashlight. When it gets hungry, thats when it will likely come out looking for food.

Good luck. Hopefully none of your other farm animals in the house would harm it if they found it.