Just because people go underground doesn't mean they don't exist. If they where killing police officers left and right and causing chaos the government would have steeped in already. Though who buys stolen cars and runs chop shops, who owns the casinos, who monopolises entire financial industries. Of course there are other people that do that though the mafia is still a huge part of the criminal underground, that exists away from the eyes of the public.
Of course its not what you will see in movies, and many people just call them selves American not Italian, it may be the same group of people but its just the Mafia now, not the Italian Mafia.
I live in the united states and the crime family's here are very dangerous nobody will speak up about crimes because of fear of retaliation but they are still alive and strong they are still creating wise guys there crimes range anywhere from petty bullshit all the way till murder
A lot of the Mafia is quiet today and you don't hear a lot about them because they are avoiding law enforcement. The Patricara Crime Family of New England was headed down hill but today they are heading back up as they are putting more guys on the streets. The Mafia isn't like the good old days. It's more of an illegal business, they don't commit murders any more.