I didn't say "totally abandon the New 52." I've NEVER said that. Why do you keep saying that I do? What I am saying is KEEP the stuff that does work with Pre-FP canon and DITCH the stuff that doesn't. In the case of the JSA, well, they can easily be reintroduced exactly as they were before Flashpoint because the "New 52 versions" of those characters were inhabitants of another Earth altogether. They wouldn't need to do much to simply say "here's the Prime Earth version of the Justice Society (with Alan Scott and his kids, Jade and Obsidian, and Jay Garrick and Wildcat II and Stargirl et al) that has its roots to WWII and has their Pre-FP adventures intact" because there are not really many Prime Earth counterparts to contradict them. The only ones I can really think of are Dr. Fate and Stargirl.
And even for those two and the JSA overall, what do you think those 10 years that were snatched from the timeline are? They're not made up adventures. They're the Pre-FP stories and canon. So, the old JSA's adventures are contained therein. So even if they introduce the JSA without those memories, at the end of Rebirth, they will be getting them back.