The merging is always of the effect in the cause. Speech is not an effect of the mind. Therefore, the organ of speech cannot merge in the mind. For instance, heat which is the function of fire originates from fuel and extinguished in water. We see the manifestation of speech ceasing in a dying man, though his mind is still functioning.
None sees the organ of speech being merged in the mind.
So experience also teaches that the function of speech and not the organ itself gets merged in mind. This Sutra intimates that the functions of all the organs merge in the mind at the time of death. Like the speech it is observed that the eye and other senses discontinue their functions, while the mind continues to act. Because the organs themselves cannot be absorbed, and because the text admits of that interpretation we conclude that the different organs follow after, i.e., are merged in the mind only as far as their functions are concerned.