I already have Wings of Liberty and apparently you can't buy the digital deluxe edition of the Heart of the Swarm expansion on the battle.net store. The reason I want it is because I want the Kerrigan wings in Diablo 3. They made a bundle including all three games with which you get the Kerrigan wings but I don't want to pay for Wings of Liberty again. So if I buy the Heart of the Swarm digital deluxe from somewhere else, will I get the wings?
The Kerrigan wings are tied to the license, not to a pre-order, so as long as you can get a valid Heart of the Swarm Digital Deluxe or Collector's Edition code, you will receive the wings in Diablo III.
The safest way to purchase it is to get the bundle from Blizzard, but since you don't want to do that, the next best is to look for a sealed copy of the Collector's Edition on eBay.