How to come back from the pipe file?
First of all,a FIFO is a blocking IO. A process blocks on reading a FIFO, that is, when you issue vim somefifo, the vim process waits until another process opens the somefifo for writing.
So you can try another process, e.g., issue echo "foo">somefifo in a new terminal, then you can do normal operation in your vim process, like ZQ to quit.