It's not as simple as "that is that." As Paddywhack stated, your opponent couldn't place there, they might be able to place elsewhere.
To clarify, depending on the action, if you didn't have to choose a target prior to succeeding, you could choose to place elsewhere.
That said, I think most effects like this tend to have an enemy target prior to the flip. The best example I can think of is Tangled Shadows on Lilith. You target an enemy model and, upon success, place a friendly model in base contact. Here, if you select a target in her bubble and flip, you are SOL, AP is spent.