I use a combination of pixelmator and topaz labs plug ins at this point. Check them out. They may fill your needs.
I would assume so. I have purchased several now discontinued apps in the past and they all are still available under "Purchased" for me, however no longer developed or updated. I don't see why they would make this one different? Unless maybe official Apple software works differently than discontinued software from other developers.
Edit: Sad to see Aperture go. I really love it. Photos feels promising now that I've been working with it for a while but I am already missing a few things from Aperture. Not enough to pay Adobe, but hoping Photos gets developed further or even some add ons come out eventually that we can buy.