Updated: We received word from 2K saying that email from support quoted below is incorrect. They are still working on the game and will put BioShock back on the App Store when it is ready. We asked for more clarification on whether or not it will be listed again so those that can play the game will be able to download it.
Update 2: 2K responded saying they delisted the game as they did not want customers to be able to download the game while it had a gamebreaking error.
It was quite a surprise last year when 2K Games announced that BioShock would be coming to iOS. With iOS 8.4, the game ran in to some compatibility issues, basically rendering it unplayable. Those with 8.3 or earlier could still get the game to work, but others couldn't, which led to 2K removing it for purchase from the App Store. However, now BioShock has been delisted completely.
To be delisted means that even if you purchased and downloaded the game before, you will not be able to do it now. That means your only access to the game is if you had the app downloaded already and are running a compatible iOS version.
If you decided that BioShock would be pretty fun to play on a mobile device and would now like to download it again, you won't have the ability to do so—even if you were using a version of iOS the game works with.
The answer as to why BioShock was delisted is still up in the air, but a user over at the TouchArcade forums reached out to ask, receiving this response from 2K:
I understand you're having issues with Bioshock for mobile gaming. Unfortunately, you are correct we don't currently have this game for mobile gaming anymore, which I know can be frustrating. The removal of the game was a developer decision. This happens occasionally, but thankfully not often.
I'm terrible sorry for this, if you purchased Bioshock for IOS and you would like a refund, Apple will be of great assistance. Since the transaction wasn't completed through us, we can not perform a full refund back to you. However you will be able to complete a refund with Apple. They will be able to do this for you.
From that response, it seems that 2K is abandoning the game when the only recourse they give is to ask Apple for a refund. Well, and the fact that the statement flat out says "we don't currently have this game for mobile gaming anymore."
However, that "currently" does not have a finality to it either, with the explanation being it was a developer decision. Are they wanting to remove it until the game is fixed or do they have no intention of returning to the game at all?
All of that is unclear at the moment, but TechRaptor has reached out to 2K for further clarification. We'll update this article if we receive comment.