The thing to consider is that the likes of Russia will not be waiting till impact to see if those launched nukes are aimed at them before launching their own ‘retaliatory’ strikes.
Something else to consider is that even a ‘modest’ nuclear exchange of a few hundred tactical nukes would probably be enough to bring about extinction level events across most of the globe.
If a nuclear power is beating up on a non-nuclear power with nukes, there can be ‘restraint’ in how many weapons get launched. When two nuclear armed powers start lobbing nukes at each other, it’s all but inevitable that things will rapidly escalate out of all control and both end up lobbing all they can at each other.
As such, any talk of nuclear war is pretty pointless, as you pretty much always arrive at the same conclusion of the end of the human race as we know it.
What's any of what you've written got to do with the fact that if a ballistic missile leaves the atmosphere it's not in anyone's air space? Which is in response to whether missiles need to have complex paths to avoid neutral countries!
The words 'nuclear war' aren't in the sentence "Ballistic Missiles leave the atmosphere so it's usually a moot point as to whether any national sovereignty is impinged!"