This was written on July 1, 2016:
http://mynhltraderumors.com/nhl-rumors-detroit-red-wings-anaheim-ducks/2016/07/01/
"The Ducks are reportedly looking for a top-six forward or maybe a top-nine and mid-round draft pick for Cam Fowler."
And this came out on July 4, 2016:
http://bleacherreport.com/articles/...around-cam-fowler-trade-kris-russell-and-more
"On June 29, Cam Fowler told ESPN.com's Pierre LeBrun he was surprised the Anaheim Ducks didn't trade him before the NHL draft."
"The Detroit Free Press' Helene St. James speculated the Detroit Red Wings could be one of the teams angling to acquire the veteran defenseman. St. James added the Red Wings would likely need to part ways with one of Tomas Tatar or Gustav Nyquist and a second-round draft pick in order to entice Anaheim."
Now I'm not saying any of these rumors were spot on for evaluating fair trade value for Fowler. But when multiple sources are estimating something like Tatar and either a 2nd rounder or a lesser roster player, and Fowler himself was expecting to be dealt, I think it's fair to say that a trade was certainly POSSIBLE.
And as to why he still hasn't been dealt, I believe Anaheim is in a stalemate with RFA Hampus Lindholm. I think his demands really took them by surprise, and they're now reconsidering whether they shouldn't just hang on to Fowler, if they can't work something out with Lindholm.
But regardless, there are other fish in the sea, and having no cap space doesn't make a trade for any of them any easier.