Assessing Oberstein's actions insofar as they relate to act utilitarianism versus rule utilitarianism; why consequentialist systems usually have rules that do not impede on personal autonomy (pushing the man in the trolley problem) - nobody would want to live in a society where they could be sacrificed as in Westerland or the prisoner exchange at any given moment because it was deemed consequentially beneficial in the long run; this is akin to one healthy individual being euthanized and his organs being donated to 5 unhealthy individuals.
Oberstein's act utilitarianism can not foster a society as a whole, independently they might seem like correct exchanges in human suffering, but that is with the understanding that the sacrifice of unwilling individuals is a necessary component of this act.
To stop the Westerland incident because you have the chance to save innocent lives would still be a utilitarian act, it would just be a rule utilitarian, the rule being that society as a whole will run better with the understanding that you not be nuked at any given moment to serve a consequentialist equation (add commentary on why/how the utilitarian calculus has to take moral action as a rule into account regardless of numerical sacrifice?)
In this framework, stopping the nukes would be the moral thing, with the understanding that any greater harm that happens downstream from the prolonged war would be due to intentionally immoral acts on the part of the Lippstadt League.
Your moral act is independent of the immoral response because the rule utilitarian position holds that a transgression on the personal autonomy of innocent individuals is not worth the societal benefit of stopping the downstream immoral act; you do not cancel the immoral act with utilitarian calculus that impedes on that personal autonomy.
It would be akin to submitting 2 million unwilling, innocent individuals to violent experimentation in order to procure medicinal understanding for the majority, the ethical principle is the same. Some people might say that this is a conscious choice in regards to people that aren't in a binary situation, and that in westerland the nukes were going ahead whether or not, and that the choice was between stopping them or allowing them a la the trolley problem, but in actuality all that's going on in this instance is that Oberstein is watching the man fall towards the rails and is choosing not to help - in the former example, 100s of millions of people might well survive illnesses if for the sacrifice of a mere 2 million, an act utilitarian could go either way, they might deem it a moral choice given their knowledge of the downstream effects and outcomes, or they might deem it an immoral one, citing that personal autonomy given their lack of intrinsic danger or their inherent 'innocence' in the situation.
Either way it's a coin flip predicated on information at the time (note, not literally, always based on that calculus).
Consider Westerland, it might well be the case that just before the nukes drop, the Lippstadt League surrender due to unforeseen consequences, the coin flip oberstein made could kill millions of innocent people for no gain, whereas the rule utiltiarian respect of personal autonomy never makes this gamble.
The rule in rule utilitarianism tries to minimize this specifically by positing that 'even if there may be instances where the sacrifice of innocent people might be a moral act in an isolated situation, it's better to err on the rule of 'respecting that personal autonomy' because the goal of rule utilitarianism is to generalize the ethical choice within a societal framework.
Also important to note that in the case of Westerland, even if you want to posit that the downstream effects of stopping the nukes would be worse for human happiness, it is relevant to show that your moral decision was balanced with the understanding that the Lippstadt League would fight to the end and attempt immoral actions; all we believe in this instance is that humans as a whole should act morally, and the Lippstadt League not doing as such is worthy of condemntation and should thus be stopped with military action; it does not allow the sacrifice of the innocent due to Oberstein's belief in inaction on this point, because to do so is to imply the moral weight of the Empire refusing to help the innocent and the Lippstadt League actively harming the innocent is equivalent.