Philosophía
"The devil made me do it"
Manhattan will simply fix time and bring everything back after a talk with Superman, and there will be a double splash page with everything -- from Action Comics #1 [which is foreshadowed in the least subtle way possible, with Superman holding a car over his head, and then not] -- to present day with cliff notes.
Expect to see the cover of Barry and Jay discovering alternate Earths.
Expect a splash page with Golden Age Wonder Woman.
Expect the classic JSA.
etc.
The pivotal moments in all continuity.
And Superman will simply remember his entire history, from the 1930s to now.
If you expect the issue to autistically go through every single point in continuity from the last 81 years over 1000 pages, well....that's not going to happen. But the gist of it will be what I mentioned above.