Dax Milne has defied the odds and expectations his whole career. He still draws an NFL paycheck. Accordingly, it's probably high time to stop undervaluing what he brings to the table.
All that said, I do not see a lot of separation between he and Roberts. Chase is an excellent receiver and the kind I think could stick on an NFL roster the way Milne has. Milne had the advantage of being the favored target of an excellent QB for an entire season--one where we were able to feast against suspect secondaries. Roberts has had to be more patient while his recent QBs have tried to develop and/or come into their own at BYU. But Chase is a terrific player.
Love to have him back, but I have zero issues with him testing the NFL waters and hope he's a huge success.