I'd say you have to re-purchase any A2A aircraft that comes in either FSX or P3D, but you should be able to load the old aircraft just fine.
The same thing happened to me a few weeks back, and now I have my new Jetline computer, preloaded with P3D v3.4.14. I used to have FSX, a bunch of ORBX scenery, and ASN upgraded to AS16, a J-3, a P-40, and a Comanche.
It took some doing, but almost all of my ORBX scenery has been downloaded and I am confident that it will work in P3D. I have installed the FTX Global Base Pack and FTX Global Vector, so all the regions and airports should go in as well. All except for my first ORBX purchase, which was the Pacific Northwest, purchased on DVD in 2012. That cannot be loaded into P3D, but maybe I can get FTX to give me some sort of deal on the P3D download.
ASN can be made to work in either FSX or P3D, so if you've bought one, you have the other. I had to buy a new AS16 upgrade, this time in P3D.
I had to buy a new, P3D, Comanche. I know it works, because I just flew it from KHQM (Hoquiam, WA) to KAWO (Arlington, WA).
I had to re-download my P-40 and J-3, and was worried if I'd ever be able to fly them again, as they are supposedly FSX only. First I followed the advice of somebody on this forum, and went to C:\Program Files (x86)\Lockheed Martin\Prepar3D v3 and then made a copy of P3D.exe in the same folder, and renamed it to FSX.exe. Then I installed the P-40 and J-3 in C:\Program Files (x86)\Lockheed Martin\Prepar3D v3\. Everything took the new A2A update. I haven't flown them, but I started up the P-40 and it ran just fine. Now I'm tempted to get the Civilian Mustang.
P3D really works great. I'm very happy with that Jetline computer.