I agree, I think Mick will save Dean from drowning.
Dean's attempted rape of Roxy probably costs him everything (even Shirley's love). He'll possibly turn up at Mick and Linda's wedding intent on destroying their happiness.
Thank goodness everyone will see Dean for what he is at last! I've seen complaints elsewhere about the second (attempted) rape, but he's got away with it once so it's entirely probable he'd try it again. I've heard that rapists are often serial offenders (and why wouldn't they be if they go unpunished and believe they've done nothing wrong).