Again, even if they were to clinch the division with more than a week to spare, they'd still likely be mathematically alive for the playoff bye during that last week, so the incentive to win will be there.
5-11 is a stretch that is not really supported by anything this team has done this year. As potent as the DBacks offense is and hot as they are, their pitching is significantly worse than the Brewers and the Brewers have been one of the hottest teams in the 2nd half themselves.
When we dream up scenarios about bad things occurring that aren't particularly likely and play up our opponents at every opportunity while dismissing our own strengths, I think it's fair to call it "dooming".