Adam from Occipital here (we make the Structure Sensor).
As of now, you can use OpenNI with the Structure Sensor on any platforms currently supported by OpenNI. We’ve also forked OpenNI on GitHub (along with many others who have done the same) to make sure it remains available after April 23rd.
For those who don’t want to compile code, we’ll also host binaries at http://structure.io/developers for OS X and potentially other platforms.
We’re working on creating new open source Structure Sensor drivers for Android, Linux, Windows and OS X (these are not based on OpenNI at all). Let us know if you’d like to contribute to that effort by sending us an email at structure >at< occipital.com.
Keep in mind that the discontinuation of active maintenance for OpenNI does not affect the Structure Sensor for iOS at all because on iOS, we use Structure SDK, not OpenNI.
Keep an eye on http://structure.io/developers, or sign up for the Structure SDK developer email list for more info.