That's how it started and was one of the big reasons why I really liked it, but things have kind of been changing lately.
spoiler (click to show/hide)
Trying to keep this brief, basically all three die saving the world. Forgot what happened to Supes, Wonder Woman gets stabbed, and Batman blows himself up after detonating a bomb (he has to be the one to trigger it) that stops something from happening. Can't remember what that is...maybe it was boom tubes. Early stories about Superman and Batman are now in World's Finest, but that book is being canned as you mentioned already.
With all this going on, Supergirl and Robin (Batman and Catwoman's daughter) end up in a boom tube that takes them to the New 52 Earth, and their story continues in World's Finest, with them taking the identities of Power Girl and Huntress. The two eventually meet up with Robin (Damien), Supergirl, and Superman and Batman before finally finding a way to get back to Earth 2.
Wonder Woman has not come back, but her daughter, Fury, is around and initially was on Darkseid's side, but switched after a bunch of shit happened, mainly with her master, Steppenwolf, getting killed pretty violently by...
Superman has come back twice now. The first time, he was a bad guy and pretty much spent a number of months just kicking the absolute shit out of all the superheroes and ruling the world. He was finally killed and then the good guys found out he was some kind of fake. The supposed real Superman was then found deep inside a hidden lab filled with Superman clones. He may be powerless now.
There is another Superman. This is a black Kryptonian was kept hidden and freed by the other superheroes. He was initially a pacifist but finally started fighting and is in a relationship with Powergirl, cuz why not?
Another Batman showed up and was revealed to be Thomas Wayne, who takes some drug that gives him enhanced strength so he can keep up in his old age. He's addicted to the drug.
With the original Superman found, they hint that someone has the power to resurrect dead heroes, so it's possible Batman and Wonder Woman will show up again.
Lois Lane died, but was resurrected inside an android body and is the Red Tornado.
Dick Grayson is married to Barbara Gordon. Dick is an average joe and Barbara is a cop. Barbara just got killed off in a recent issue.
John Constantine is now on Earth 2 (why I don't know, it's from his own series which I still need to read) and looking for a way back. When some big tidal wave is coming and people get on a train to escape, Dick gives John his kid and stays with Barbara's corpse because I have no idea why.
Mr. Terrific, from the New 52, is also on Earth 2 for whatever reason. We know he makes it back to the original Earth because of the Future's End biweekly book. In fact, if that's canon and not something that they end up making irrelevant (the future gets changed, blah blah blah), all the Earth 2 people end up on the original Earth as refugees from the Darkseid war.
The other notable heroes are Green Lantern (Alan Scott- who is now gay, but that is pretty much meaningless since his boyfriend got killed immediately and there's no other mention of his sexuality until his boyfriend comes back as an Earth elemental and holy shit this is getting complicated), The Flash (Jay Garrick), Hawkgirl, and Dr. Fate, but despite playing a big role previously, over the past year or so the focus has shifted to Earth 2 Batman, Superman, Red Tornado, and crew, although it is an ensemble book.
The last issue of Earth 2 also saw Huntress get turned into one of Darkseid's furies.
