Assuming this happens after Bragg's attempted command purge at the end of Chickamauga, who of the proper grade and rank (which eliminates candidates like Forrest and Cleburne) did Davis have to replace Bragg?
- Gen. Robert E. Lee: Nope, Davis asked, Lee said no.
- Gen. Joe Johnston: a man which Davis hated with his feud over his secrecy and petty jealousy over rank, pretty much a last resort for Davis
- Gen. P.G.T. Beauregard: the only man Davis hated even more than Johnston and was openly critical of the government in the press. No sell
- Lt. Gen. Leonidas Polk: though Bragg was a close friend of Polk's, I think even he had sense that Polk was not a general. Not to mention that Polk himself advocated for Johnston.
- Lt. Gen. William J. Hardee: declined the post repeatedly, why would he change now?
- Lt. Gen. Longstreet: an outsider of the Army of Tennessee, his motive for the removal of Bragg was to get Joe Johnston in command of the Army of Tennessee, so Longstreet's not much of a contender
Not exactly a sterling set of candidates for Davis to choose from. Given that Johnston sought for alternatives before finally deciding on Johnston, I think Leonidas Polk would be in command of the Army of Tennessee, and considering how the Army of Tennessee was in seemingly good condition, I don't see why Davis would have any incentive or impetus to replace Polk with Joe Johnston.
Leonidas Polk was completely lacking in tactical articulation, professionalism and proper subordination. Polk at the helm of the Army of Tennessee? Shudder the thought!