In today's society, you will need both. You will have people who want to use self-service but then there are people who want to interact with people. I currently have plans to use both. The Self Service for the ones that have been there for a long time and know what they want or the ones that don't want to wait in line. The cashier is there to help decide what the customer wants or if it's the first time that they are there.
My opinion is that machines can replace cashiers in retail stores, the self-checkout solution is a good example. It is convenient and quicker then cashier's service.
But for cafes and restaurants, it is possible only partial because most people like to talk with barista or bartender. People need more than just mechanical service. Peoples' communication is very important.
As the example, you can watch a video about Cafe X robotic coffee shop, which was open in San Francisco in 2014. This is a coffee shop innovative model. Yes, it interesting and fashionable today, but it will never replace live humans.