They will have to deeply research about Bitmixer and clarification from the mixer's owner and reasons of self-closing the mixer in 2017. I believe the Bitmixer owner consultation with his lawyers and his deeply thinking before closing down that platform will be serious enough for other mixers' owners to think about their services.
Bitmixer owner said that he contacted his pastor, not his lawyer but this is bullshit. He smelled that it was dangerous to continue to operate Bitmixer.io and when he saw that so many people got arrested in 2016-17, he decided to shut down his service. He is the one of the smartest guy out there who knows when to start and when to stop. Bitmixer was a real money making machine.
Why do you all think that Bitmixer owner was stupid? Mixer over mixer is created every day with the same algorithm, no significant improvement. Blockchain analysis companies are getting better and better. If it was impossible to arrest someone 6 years ago, now it's possible to easily catch with the help of blockchain. Blockchain is not an unreadable book anymore. Bitmixer owner suggested everyone to move on Monero if you want privacy and full anonymity, everything is clear.
Want privacy without being in panic all the time? Use Monero.
Want doubtful privacy and being in panic all the time? Use mixers.
Choice is yours!
Mixers will find another way to advertise their platforms, bitcointalk was not their only platform. They might still be able to bypass restrictions because there doesn't exist any restriction without loopholes. What about only this text in signature without ahref link? Sinbadio platform for your coin safety. It's still an advertisement, just simple text but easy to understand what website to visit for those who know ABC in computer and internet.