He drops out of sight after September, 1861.

William F. Gaines, age 34, Captain, Capt. William F. Gaine's Company (Gibbb's Confederate Guards), Bonham's Regiment, Mississippi Vols.,* joined for duty and enrolled for the war, June 1, 1861 at Vicksburg, Miss. with the 22nd Mississippi, signed a requisition July 4, 1861 for rations and camp equipage at Camp Clark, Corinth, Miss. for 68 men as Capt., Warren Vols., Bonham Regt., and also for 74 men of the Morton Pine Knot/Knob, mustered in at Iuka, Miss. July 27, 1861, receipted for pay September 1, 1861 at Memphis, no further records

* This company appears to have been broken up soon after its muster into the service of the Confederate States and most of the men were assigned to various companies of the 21st Regiment Tennessee Infantry

...

Officers of Gaines' Company (Gibbs Confederate Guards,
erroneously called Company K)

William F. Gaines, Capt.
A. J. Gibbs, 1st Lt.
Aaron A. Cox, 2nd Lt., to 1st Lt., Company G, Twenty-first
Tennessee; Capt., Ninth Confederate Infantry
M. [or N.] Hockett, 2nd Lt.
List dated December 16, 1861 filed with Twenty-first Ten-
nessee Infantry shows names of thirty-seven former members of
this company serving in various companies of that regiment (all
are identified as of this company on muster-in rolls). Nine others
are identified as Company G, Twenty-first Tennessee Infantry,
among where Second Lieutenant A. A. Cox is found to have been
made first lieutenant. Twenty-four of these are found to have
been assigned to Company G. From above data, it is evident that
Captain Gaines' Company was broken up soon after organization
and most of the members of company transferred to Twenty-first
Regiment, Tennessee Infantry (number and date of order not
found).

[Note - He does not appear on any of these orgainzations]

M269: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Mississippi