While it's true that about 99% of people listed in the panama papers got off scott free... There were still some serious consequences for some... and those consequences might just be enough to deter.
Some insights from a person who has worked for two years for an investigative journalism organization (that was a part of both Panama Papers and Paradise Papers, but I left my position months before Paradise Papers):
If someone's gonna kill an investigative journalist, he's not gonna do that while she's reporting on the story. That would be too dumb and raise way too many eyebrows. Instead, the attacker will usually let it cool down and wait, months (or possibly years) after the piece was published. Only when the thing is in the far past will he attack. Plus, the observation and preparation of the attack doesn't happen in a day[0].
So, I guess what I'm trying to say is that, whoever was behind the attack, was either a) stupid or b) a person that she reported on a relatively long time ago.
[0] For a case in point, take a look at how precise was the action in which a Belarus journalist was killed in 2016: https://www.youtube.com/watch?v=liSa5OFCkf4&feature=youtu.be... (the entire video is 49 minutes long, but the relevant part is about two minutes long and it starts where the link leads to)
