Does the split brain disprove a materialistic mind? According to materialism, the conscious mind is the product of the brain.  Thus, if the brain is split in half such that the two hemispheres cannot communicate with each other, then there are three possibilities:


Both hemispheres gain their own conscious mind.
Only one hemispheres has a conscious mind.
A single conscious mind operates across both hemispheres.


Within a materialistic paradigm, #3 is impossible.  There cannot be unified control without communication between the two hemispheres.

Option #1 is false according to this article,


  A new research study contradicts the established view that so-called
  split-brain patients have a split consciousness. Instead, the
  researchers behind the study, led by UvA psychologist Yair Pinto, have
  found strong evidence showing that despite being characterised by
  little to no communication between the right and left brain
  hemispheres, split brain does not cause two independent conscious
  perceivers in one brain. Their results are published in the latest
  edition of the journal Brain.


and this answer.


  So I conclude from [sic] this quick literature review that Joseph
  ascribes the presence of two minds based on something that can be
  explained at a more basic level, and hence by a more simple model,
  namely disinhibited motor control. Given the principle of parsimony, I
  conclude his observations were right, but that his conclusions were
  not.


Option #2 is false according to this answer.  The answer state consciousness does not transfer to one half, but continues to operate in both halves.


  If by continuity you mean, "a feeling that I am who I was before the
  operation, (perhaps with some changes)", then it seems that each
  hemisphere would separately maintain continuity, in the same way
  patients after massive strokes and other sudden brain injuries don't
  usually feel "they are a different person".


Thus, only option #3 is viable according to the available data.

If option #3 is indeed the only possible explanation, yet is impossible according to materialism, then the materialistic explanation for the conscious mind is false.

A fourth possibility is there is an alternative communication pathway that is not severed, as hinted at by this answer.


  Keep in mind that there are many other pathways between the
  hemispheres besides the Corpus Callosum - such as thalamocortical
  circuits, those via the midbrain and brainstem and of course external
  sensorimotor feedback.


Is option #3 the only viable option, or do the halves somehow communicate in a different way?
The question title reads:

Does the split brain disprove a materialistic mind?

The simple answer being no, nothing disproves that - the brain harbors the mind e.g., (Lilienfeld &amp; Arkowitz, 2008).
Now you mention that two hypotheses on split-brain patients are false, namely...


Both [hemispheres] gain their own conscious mind.

Only one [hemisphere] has a conscious mind.



...and I agree with them being incorrect hypotheses as suggested in the linked pages.
Now you proceed with...

[Does a] single conscious mind operates across both [hemispheres ?]

Importantly, you state yourself that...

[...] there are [...] other pathways between the hemispheres besides the corpus callosum - such as thalamocortical circuits [...] and those via the midbrain and brainstem [...].

So from my perspective, up until now you have answered your own question whether one single mind operates across two hemispheres in split-brain patients. Anyway, to illustrate some additional interhemispheric commissures besides the callosal pathway, see Fig. 1. This shows that 'split-brains are in fact not entirely split; only the main causeway is severed.
Now there are wild stories about split-brain patients having a dual consciousness, including the paper by Joseph (1998) where the author speculates that one of his patients &quot;...was possessed of two minds&quot; based on the frustrations experienced by this person because his motor skills were erratic. Andrew &amp; Akelaitis (1945) explain that split-brain patients can display diagnostic dyspraxia by an unbalanced inhibitory influence of the dominant hemisphere over the non-dominant side, explaining the uncoordinated behavior on the non-dominant side. These symptoms generally diminish over time, as the brain deploys alternative inter-hemispheric routing of communications.

Fig. 1. Interhemispheric pathways are indicated by numbers 1, 2, 3 and 4. source: Urbanski et al. (2014)
References
- Andrew &amp; Akelaitis (1945) Am J Psychiatr; 101(5): 594-9
- Joseph, J Clin Psychol (1988); 44(5): 770-9
- Lilienfeld &amp; Arkowitz, Sci Am Mind (February 2008)
- Urbanski et al., *Front Integr Neurosci (2014)