No way, lots of new expressions are originated on internet. On the other hand, there are many words and expressions that are no longer used. For example, many words that my grandparents say aren't used anymore among younger people and even their meanings aren't known for us.

I would say no, I am an English native but I still am learning new vocabulary in my own language all the time.

I think it doesn't, no matter how proficient you become, there's always something to new to learn.