I'm thinking Cavill will do:
Man of Steel
Batman v Superman: Dawn of Justice
Justice League: Part One
Justice League: Part Two
Affleck will do:
Batman v Superman: Dawn of Justice
Justice League: Part One
Justice League: Part Two
Gadot will do:
Batman v Superman: Dawn of Justice
Wonder Woman
Justice League: Part One
Justice League: Part Two
And then the rest of the announced cast will carry it all from there, leading into more B-list heroes and establishing Justice Society, and expanding Justice League Dark. Then... reboot the entire thing again from scratch in 15 years. Rinse and repeat.
I think once these other characters are established and in the public's consciousness, we really won't need the Trinity. That sounds sacrilegious, but it's basically the same thing with Marvel. RDJ, Evans, and Hemsworth will all be gone, so will Ruffalo, so that wave of actors is paving the way for Black Panther, Captain Marvel, Doctor Strange, Ant-Man, and the Inhumans to carry the universe. At that point, you don't NEED Iron Man, Cap or Thor. Same with DC.