It should not have starved to death or died of thirst in two days, since newly hatched mail order chicks are often in the mail for 2-3 days...
I'm sorry, but I don't know what to tell you - of all the chicks we've hatched here, we've only had one die, and I never knew why it died. It was fine in the a.m. and then dead in the bedding when I got home (it was only a day old). There are just so many "maybes and whys and what-ifs"... The chick could have gotten pecked. It could have ingested a large piece of bedding. It could have had a congenital defect. The list goes on and on...
If you're home most of the time, then I would just do frequent checks and take time to observe to make sure the moms are being motherly (make sure the food/water dish is super close to the brooding moms). Sprinkle bits of crumble around the mom/chicks and see if one of them begins calling the chick to eat (that is a good sign). But if you work outside the home, and are worried, then take them as they hatch and brood them yourself.