...how do you explain, that not every loss of separation situation inevitably lead to a mid-air?
OK. "Separation" in an ATC sense means the horizontal, vertical and time buffers between aircraft. If any of these becomes less that the proscribed value for the type of airspace/aeroplane/service, etc. then there has been a "loss of separation". This does
not mean that there has been/will be a collision, simply that the "protected area" around an aircraft has been infringed. If the limit in a particular scenario is 5nm and the aircraft come within 3nm of each other, then that is a "loss of separation"; On the NATS 10 minute separation is applied with 1,000' vertically and 60nm laterally (well, a bit less as you are allowed to offset) - if you end up 8mins apart, action is taken to increase the separation again.
why don't we hear about more mid-air collisions over Africa in the news?
We fly offsets and make position reports to each other on a common frequency. Conflicts are often discovered and managed by the pilots and may not involve ATC at all...
Perhaps the introduction of full-duplex digital communications and transmission of digitized instruction, with person-to-person communication being an exception for uncommon situations could help, but their impact on aviation safety is still unknown.
This sort of thing has been slowly coming for quite a while. We use ADS & CPDLC in remote areas quite a bit now, and are trialling them in the Maastrict FIR. I think we also did a FANS flight from the Southern USA on a direct track to the holding fix in the UK. It's getting there.