Dhawan's slump has come at a terrible time for India, and puts him in a position where he can possible have no real role in the WC.
If India were starting against the minnows, then we could stick with him and hope that he could have found some form as he went along. However with India starting off against the two of the toughest sides in the group in the first two matches, India cannot hope that Dhawan will suddenly find form.
So India kinda have no option but to start with Rohit and Rahane. If they kick off and do well, then there is no reason to go back to Dhawan. Even if they don't do well in the first two, Dhawan is so out of form that India will then given Rohit and Rahane the matches against the lesser sides to find their form.
So either way, barring an injury, and perhaps even then, Dhawan has already put himself in a position where he can be nothing more than a passenger on the tour. At best he could get a game if India have already qualified or so on, where again he is not really making a meaningful contribution.
In a squad of 15 for there to be 2 rather clear passengers, Binny being the other one, is not really the strongest of squads. Its infact quite liekly that Binny could actually make a bigger contribution than Dhawan, and who would have thought that possible when the squads were announced.
In fact speaking of Binny as long as Binny gives us around 25 runs an innings he could still prove to be invaluable. As for Dhawan, I think India need to find a way to use him, and there is no point in him being a passenger. If he cannot contribute right at the top, then India must try him in the middle order against an older ball. Remember his finest knock on the tour so far was when he was not batting right at the start.
Dhawan has some shots and could perhaps be useful lower down the order in the 35-50 over period. I think India should try that option in the final game against England.