It should work without a phone connection, since it's all based on credit card numbers which are transferred through the terminal and not a data connection. If it works like the Apple Watch and Apple Pay, you should be able to pay without a connection to a phone or data network.Yeah, I think this is my next smartwatch.
As for Samsung Pay without a Samsung phone, good question. For me, I have the Note 7. However, friends have Nexus's and Motos so we'll see...