What is the deal with the possibility of it being discontinued? Is that possibility real? (February 2015)
If so what would be an alternative photo application for my iMAC?
Yes, Apple has announced, that there will be no further development of Aperture. That means, we will not see a new, paid upgrade Aperture 4, only bug fixes and compatibility updates to Aperture during the life cycle of Yosemite.
And it is the last chance to buy Aperture, if you want it. Once Apple releases a new operating system, that no longer supports Aperture or iPhoto, it will no longer be possible to buy it.
I am considering purchasing Aperture.
It may be worthwhile to buy Aperture now, if you already have compatible photolibraries, as a long time iPhoto user. Migrating from iPhoto to Aperture is simple - just open your iPhoto Libraries in Aperture and you can use all advanced features or consolidate your iPhoto Libraries.
Aperture 3.3: How to use Aperture to merge iPhoto libraries
But if you are currently using other photo software, it will probably too much work to invest into Aperture this late.
Apple will release a new Photos.app for the Mac later this year. I would wait, what this software will be like. We do not know anything about it yet.
If you have to migrate now, look at Capture One Pro or Lightroom, digicam, just browse the web. I am reluctant to use any third party software, that does not integrate well with the Mac ecosystem.
Top 10 Reasons Why I Chose Capture One Pro over Adobe ...