Actually, it would need to provide a rather sheer wall, since its been claimed the ice wall "cannot be scaled." It would also need to be massive enough to contain the "atmolayer." The pictures you refference (and I see none of them) probably do not exhibit these necessary properties.
The 150 foot Ice Wall was discovered by Sir James Clark Ross, a polar explorer who was among the first to venture to Antarctica in an attempt to determine the position of the South Magnetic Pole. Upon confronting the massive vertical front of of ice he famously remarked
"It was ... an obstruction of such character as to leave no doubt in my mind as to our future proceedings, for we might as well sail through the cliffs of Dover as to penetrate such a mass.
It would be impossible to conceive a more solid-looking mass of ice; not the smallest appearance of any rent or fissure could we discover throughout its whole extent, and the intensely bright sky beyond it but too plainly indicated the great distance to which it reached southward."
Beyond the 150 foot Ice Wall is anyone's guess. How far the ice extends; how it terminates; and what exists beyond it, are questions to which no present human experience can reply. All we at present know is, that snow and hail, howling winds, and indescribable storms and hurricanes prevail; and that in every direction "human ingress is barred by unsealed escarpments of perpetual ice," extending farther than eye or telescope can penetrate, and becoming lost in gloom and darkness. Some hold that the tundra of ice and snow stretches forever eternally.
Edge of the world:
http://uwamrc.ssec.wisc.edu/images/gallery/B15Aedge.jpgTemperatures approach absolute zero the further one explores outwards. Exploration in this type of pitch black freezing environment is impossible for any man or machine. We live on a vast plane with an unknown diameter and an unknown depth. Dr. Samuel Birley Rowbotham held that knowing the true dimensions of the Earth is something which will be forever be unknowable by man.
The Flat Earth does not necessary need to be physically infinite in order to contain the atmosphere - just very big. Often we might hear "infinite earth" from Flat Earth proponents as an analogy for what exists past the ice wall; a stretch of land incomprehensible by human standards.
In order for barometric pressure to rise and fall, an element of heat must be present. Heat creates pressure. A lack of heat results in a drop in pressure. These two elements are tightly correlated in modern physics.
In our local area the heat of the day comes from the sun, moving and swashing around wind currents from areas of low pressures to areas of high pressures with its heat. The coldness of the Antarctic tundra keeps the pressure low. Beyond the known world, where the rays of the sun do not reach, the tundra of ice and snow lays in perpetual darkness. If one could move away from the Ice Wall into the uncharted tundra the surrounding temperatures would drop lower and lower until it nears absolute zero. Defining the exact length of the gradient would take some looking into, but at a significant distance past the edge of the Ice Wall temperatures will drop to a point where barometric pressure nears the zero mark. At this point, whether it be millions or hundreds of millions of miles from the edge of Ice Wall, the world can end without the atmosphere leaking into space.
The atmosphere exists as a lip on the surface of the earth, held in by vast gradients of declining pressure.