I think it can be a tricky question. We're essentially being asked to look at a chain of events and say that the decision a politician made caused 1000 deaths. But how far back can we take the chain then? If that politician ran a campaign on cutting government spending shouldn't the voters who elected them have a measure of culpability then?
Since lives are going to be lost within the tenure of a government administration in a myriad of ways, do we have to do some kind of "net mortality" calculation? If cuts were made to fire inspection but a budget increase was granted to infectious disease research that resulted in saving 50,000 lives would the politician get a pass?
It's a tricky and touchy question. I do think that when there is evidence of gross negligence or outright abuse(kickbacks for construction contracts, etc.) absolutely yes... prosecute. We're actually seeing this happen here in the US where officials in charge of the Flint Michigan water supply are facing manslaughter charges for their actions.
Very well put. I think that is true it is definitely a difficult subject to come to a final conclusion on. Your hypothetical example is a good one.