Big Arnie has went on record saying....
“I think it’s cool to continue on with the franchise,” he said. “In case I want to jump over again and get into the acting after I’m through here.”
Now this either A: surprises you as you thought the big man was done with the whol franchise or B: fully expected it after reading that Arnie has a cameo in Salvation 1.
(Minor spoiler below)
From what we know the new film is as much about Skynet harvesting humans to learn how to grow flesh and eventually building the T-800 as it is about John Connor and the human resistance so Arnie's model T-800 will have to be in the series if it continues. All you have to do is know the basics of the franchise plot history. A T-800 is captured and sent back by Connor himself and another is responsible for Connors murder so unless digital face mapping becomes indistinguishable from real people then he will be there.