This makes perfect sense as Hailey was gone by Oct and replaced by CPT Hayhurst. However, not sure what happened to him. I do know that many men of Hawthorne's unit were at Camp Hope/Nelson and died there, so perhaps Hailey was there and died at that time (Aug-Oct) I know that by Nov they had already made the move to Ft Smith/Van Buren area and most of the Saline Co. men in Hawthornes died in Aug and Sept there at Austin.

10/19 Fayetteville, Hdqrs. Dist of Ark #18
...
Col A T Hawthorne is assigned to the command of the Bn composed of companies of Dawson’s, Tumlinson’s, Perkins and Hay...est (Hayhurst perhaps?) Co’s of [of Brooks brigade]