I think that if the government really wants to get you, they will find a way. Take the almost 70.000 BTC that were seized from the hacker Individual X a few days ago. It took years, but they did it. He used tumblers/mixers but was still caught in the end.
It's definitely possible to get caught, but definitely also possible to get away with it if you do things right. Tumbling/mixing your coins doesn't automatically mean that your coins are now untraceable(probably a huge misconception), as you could still fuck it up by doing things like re-joining coins and such.
Even though the coins have been broken down and then combined again, but I think if the government tries to trace it, I don't think it's a difficult thing. but sometimes we collide with the legal regulations established in each country, so that it cannot run according to personal desires