Katha-2-2-4-asya visraṃsamānasya

Sri Shankara’s Commentary (Bhashya) translated by S. Sitarama Sastri

Com.—Again, of this âtman in the body, visramsamânasya ] escaping. Dehinah ] embodied. The meaning of the word visramsamâna is explained by the expression dêhât vimuchyamânasya (being free from the body); what here remains? nothing of the whole lot of prâna, etc., remains. Here] in the body; the âtman, on whose leaving the body, all this lot of effects and causes becomes in an instant enervated, destroyed and defunct, as in the case of the inhabitants of a city, when the lord of the city, is driven out of it, has been established to be some other than all this.

Links
Various resources on the Kathopanishad
Upanishad Series – Katopanishad Commentary by Swami Chinmayananda