First, current users can just do what they have been doing and continue using Aperture as it is. The program works fine now. Ending development doesn't mean the program will stop working. It just won't get any future enhancements. Aperture is still the same program it was last month. Go ahead and keep using it. While our at it go read my article and make a great looking book ;-)
The second option for Aperture users is that they can migrate over to a new application Apple is releasing for Mac OS X called "Photos". The details are still scarce. But this program is replacing both Aperture and iPhoto and I believe is supposed to come out this fall when OS X Yosemite is released.
The third option for users is the option to switch to an alternative program such as Adobe's lightroom app. I've been testing this a little bit.For now I personally am going to keep using Aperture until more details about the features of the new Photos app come out. Aperture is supposed to get one more update to make it compatible with Yosemite theoretically making the program usable for number years to come, if you so choose. Unfortunately the announcement of Aperture's end will probably limit or possibly end the articles I put out about Aperture in the future. I'm still waiting to see how Aperture Expert will move forward. I'm hoping the subject of behind the scenes workflow will continue to be at the heart of the website. If it is I hope to continue contributing there in the future. If you made it all the way to the end of this article then you probably care about Aperture. Go check out ApertureExpert.com because Joseph has done a terrific job talking about what the end of Aperture development means and what the possibilities are for the future.