Nylea, God of the Hunt will still be attacking. There is no time in this situation when Alpha's devotion to green is less than five. For anyone who hasn't read the Cranial Insertion article, it's effectively exactly the same, only it uses Banishing Light instead of Vedalken Shackles, which changes the answer–in that case, Nylea
does briefly stop being a creature, and is removed from combat.
The difference between these two scenarios is that Vedalken Shackles works by applying a continuous effect, while Banishing Light performs a one-shot action and tells you to perform a second one-shot action immediately
after some other event occurs. (See CR610.3.)
Compare the game state immediately after Vedalken Shackles is destroyed to the game state immediately after a Banishing Light is destroyed, before any other actions are performed in either case.
Immediately after Vedalken Shackles is destroyed, Alpha controls Nylea and Swordwise Centaur, and we also have a Kalonian Tusker sitting on the battlefield. Who controls that Tusker? Alpha does, because no continuous effect exists that might change that. So Alpha has a devotion to green of 5, and Nylea is active.
On the other hand, immediately after Banishing Light is destroyed, Alpha controls Nylea and Swordwise Centaur, and there's a Kalonian Tusker sitting in exile. Alpha therefore has a devotion to green of 3, so Nylea is not a creature and is therefore no longer in combat. (See CR506.4) The very next action that will occur in the game will put that Tusker onto the battlefield under Alpha's control, but it's too late–Nylea's no longer attacking.
Edited Callum Milne (Jan. 20, 2015 04:32:03 PM)