Consider the spell wall of ice (PHB, p. 285), specifically these sections (emphasis mine):
You create a wall of ice on a solid surface within range. You can form it into a hemispherical dome or a sphere with a radius of up to 10 feet, or you can shape a flat surface made up of ten 10-foot-square panels. Each panel must be contiguous with another panel. In any form, the wall is 1 foot thick and lasts for the duration.
...
The wall is an object that can be damaged and thus breached. It has AC 12 and 30 hit points per 10-foot section, and it is vulnerable to fire damage. Reducing a 10-foot section of wall to 0 hit points destroys it and leaves behind a sheet of frigid air in the space the wall occupied. A creature moving through the sheet of frigid air for the first time on a turn must make a Constitution saving throw. That creature takes 5d6 cold damage on a failed save, or half as much damage on a successful one.
One of the elemental disciplines of a Way of the Four Elements Monk is "Shape the Flowing River", which does the following (PHB, p. 81; emphasis mine):
Shape the Flowing River. As an action, you can spend 1 ki point to choose an area of ice or water no larger than 30 feet on a side within 120 feet of you. You can change water to ice within the area and vice versa, and you can reshape ice in the area in any manner you choose. You can raise or lower the ice's elevation, create or fill in a trench, erect or flatten a wall, or form a pillar. The extent of any such changes can't exceed half the area's largest dimension. For example, if you affect a 30-foot square, you can create a pillar up to 15 feet high. raise or lower the square's elevation by up to 15 feet, dig a trench up to 15 feet deep, and so on. You can't shape the ice to trap or injure a creature in the area.
Let's say an enemy spellcaster casts wall of ice to block the party (let's say to stop the melee party members from closing in on them), and the party's Monk uses "Shape the Flowing River" to turn a chunk of that ice wall into water, thereby partially removing the obstacle and allowing the party to charge in.
Firstly, can this be done? I don't see any reason why not. The spell makes ice, and the discipline turns ice into water. This part seems pretty clear to me.
Secondly, and is the real question I'm asking here, if the ice it turned to water, does it still leave behind the "frigid air" that does 5d6 cold damage as per the spell's description?
The reason I think it might not is because the wall wasn't reduced to 0 hit points, it was simply turned into something else. On the other hand, it might because you could argue that the wall was destroyed in the sense that it's no longer a wall, even if the ice it was made of wasn't reduced to 0 hit points, and thus it would still leave behind the "frigid air".
What would the RAW outcome be, as best as can be deduced from the text?
