The mantra is not talking about rolling the sky, it's just used in analogous comparision:
निष्कलं निष्क्रिय शान्तं निरवद्यं निरञ्जनम् ।
अमृतस्य पर सेतुं दग्धेन्धनमिवानलम् ।। 19
यदा चर्मवदाकाशं वेष्टयिष्यन्ति मानवा ।
तदा देवमविज्ञाय दुःखस्यान्तो भविष्यति ।। 20
When men shall roll up space as if it were a piece of hide, then there will be an end of misery without one’s cultivating the Knowledge of the Lord, who is without parts, without actions, tranquil, blameless, unattached, the supreme bridge to Immortality, and like a fire that has consumed all its fuel.
It doesn't mean one can roll up the sky. It means just as it is never possible to roll up the sky as a piece of leather, in the same way it is utterly impossible to put an end to miseries of the world without the
knowledge of the Lord.
Here is what commentary of AdiShankara tells about this verse (although it is debated that whether Shankara wrote commentary on this Upanishad or not):
This is a beautiful way of explaining a difficult topic. The Mantra says that just as it is never possible to roll up the akasa (sky) as a piece of leather (like a piece of suit-length cloth) so it is utterly impossible to put an end to miseries of the world without the knowledge of the Lord. Only when something impossible happens will misery cease without one’s realizing God in one’s heart. That God has been described in various terms. Brahman is free from the slightest trace of
phenomenality. It is like blazing charcoal which burns radiantly after the wood is consumed.
Bhagavad Gita says:
naadatte kasyachit paapam na chaiva sukritam vibhuh
ajnaanenaavritam jnaanam tena muhyanti jantavah //5.15 //
Nor does the all-pervading Spirit take on the merit or demerit of any. Knowledge is
enveloped in ignorance and hence beings get deluded.
jnaanena tu tadajnaanam yeshaam naashitamaatmanah
teshaam aadityavajjnaanam prakaashayati tatparam // 5.16 //
But to those whose ignorance is destroyed by the Knowledge of the Self, that knowledge,
like the Sun, reveals the Supreme (Brahman).
tadbuddhayas tadaatmaanas tannishthaas tatparaayanaah
gacchantyapunaraavrittim jnaana nirdhoota kalmashaah // 5.17 //
Fixing their minds on Him, at one with Him, abiding in Him, realizing Him alone as the
Supreme Goal, they reach a state, from which there is no return, their sins having been
destroyed by their Knowledge.