Yeah, let's just measure the density and composition of a comet that will be here in a few months, and with expectations that it may be releasing new gaseous formations as it gets closer, predict what will happen with those formations.
In much simpler form, it's similar to the "Where will this satellite in a decaying orbit land?"
The difficulty is not the approximation: the difficulty is that whether drag begins to increase at t=x or t=x+30sec (based on orientation when it first encounters atmosphere) cascades throughout the rest of the equations and dramatically changes the results.
Let me just code that up real fast.