Volatile solutes follow this exact process, with measurable half-lives. It is also trivial to construct a model of an evaporator in which the surface area decreases linearly with the remaining volume - an inverted conical evaporation chamber - and therefore even simplistic calculations like dV/dt = -kS will yield an exponential decay along these same lines.

The issue of these processes continuing in perpetuity (hi Zeno) isn't an issue with any non-zero threshold, as there are closed form solutions for the problem.

Primarily, however, this is a coding site and it's perfectly acceptable to have unrealistic kata.

This complaint is both factually wrong and just plain ridiculous.