When victims are not found more than 24 hours, the chances of them getting found alive is pretty slim. It rarely happens that a victim will show up with just bruises and can go on with their lives after. But this one has $3.6B, I don't think a criminal will let them go without a truckload of money.
Most of the users were early adopters of Bitcoin, and that's how they managed to own that many coins. BTW, the owners claim that their life is under threat. But I don't think that is the case. They have already fled to the United Kingdom, and may soon make an application for asylum claiming that their life is under threat. The claim that they were threatened is just an excuse to make their case strong before the asylum application. And given the circumstances, any chance of the UK government deporting back to South Africa looks slim.