If the chick got through the wire (I've had one get through 1"x2" wire), it would be easy pickings for predators. The chick I had that escaped through the 1"x2" wire was taken by a hawk that was lurking around, just waiting for an opportunity. :hmm
Sorry to hear that you lost a hatchling. :(
Is your broody in a secure setting, or could some type of predator have gotten to the chick? There are a number of animals that could squeeze through even very small openings.