Even if X-Com knew all that, it is not within their power to do anything about it. Even if they assassinated everyone involved, what would come of it? You can't topple a modern state machine by offing a president, things haven't worked this way since antiquity.
The previous story was along similar lines, but it was stretched really thin, especially for something that's supposed to happen multiple times per campaign. For a single mission this might work using lots of plot, special circumstances, allies etc., but definitely not as a generic thing.
I am not suggesting assassination, but removal of MC, if present.
In what I am proposing, killing the person responsible would just give a massive point penalty (let's say -500 000) and
not return the country.
Abducting them would give (judging from how I get about 20 000 points per month) -30 000 points. They could then be interrogated and would give one of:
1. Mind control cleared off head of country A. Country A resumes funding.
2. Head of country A was not mind controlled. Country A does not resume funding and other council members are furious. -10 000 points.
Due to research involved, there would have to be a separate unit, mission, and research topics for each country and it would still only be performable once per country with success not guaranteed.
Edit: It is fine if there is now way to get countries back. I am just saying how it could work if there was a way. It would be costly and on failiure potentially devastating to X-Com, as they obviously can't go around killing or abducting world leaders.