Di Maria is unique in his own right the way Vidal is. To find a winger that has that skill and work rate is rare just like Vidal's defensive + offensive abilities are rare. Also left footed which is even more rare.
Di Maria can play in 4-2-3-1, 4-3-3, 4-4-2, and I wouldn't be that scared with him in a 3-5-2 against weak teams as he sometimes plays there for Real when chasing a goal.
For me, if they want to sell Di Maria, I just forget about Higuain and start talking Di Maria.