As for the person or people behind this getting caught, then as mentioned above, it all depends on the mistakes they might[1] have made in the past, or are going to make.
If the hacker is very good at stealing, catching him will be very difficult, he knows to be very careful about how he moves the coins.
Difficult is not the same as impossible, as time goes on, there would be a mistake that would link the transactions to one or more real identity, that is where the apprehension of the culprits would begin. It might take time, but it is still possible. My greatest concern is that recovered funds rarely go back to the victims, the government takes it, which makes it look like the government recovers such funds in its own interest.
Mixers are a very good way to close the trace. They can make use of different mixers, split across different receiving addresses with unequal amounts and different timing, it will be hard to trace all the coins to a particular source.
Mixers which tampers with this funds are just putting themselves into unnecessary trouble, the government would not fold their hands and watch them continue to exist. IMO they should blacklist those addresses bearing the stolen funds not to draw unnecessary attention to themselves
