HELP! Baby chick with new head injury
General treatment for wry neck is VitaminE with Selenium.
Here is more information on vitamin products, foods and wry neck syndrome:
I'm sorry for your loss
Unfortunately it is hard to pinpoint the exact cause of loss sometimes.
Some chicks just fail to thrive. It could have been so many things, from neurological/developmental disorders, vitamin/nutrition or some type of unknown illness.
Unless your other chicks start showing signs/symptoms similar, then there's really no way to start putting the pieces together.