For what it's worth my mind's been working the same way, Infinity. I've always felt that Ra's and Harvey could easily be explained away as "not dead" without any difficulty. They never actually said that Harvey was dead. It was absolutely implied, but not explicitly stated. And Batman survived the same fall.
Ra's is a ninja master and overall tricky bastard... and we never saw his body. So like you said, anything's possible there.
The casting call for a female lead has me thinking about Talia, of course. It would be the perfect way to re-introduce Ra's al Ghul.
Man, I can almost imagine a scenario where there's a price on Batman's head and a bunch of assassins and thugs are after him. Including Deadshot. Then Talia shows up as this mysterious femme fatale who bails Batman out of a tight spot and he's distrustful of her but she's interesting, dangerous and beautiful and she leads him on some wild-goose chase that ends with Ra's, alive again, with some crazy-ass choice for Bruce to make.
More food for thought - and some of you will call me crazy, and that's okay, none of this claims to be anything other than me having fun - but you know, in the original article where the title was announced, Geoff Boucher mentions Nolan having told him that the title of "The Dark Knight" referred as much to Harvey as to Bruce.
So would "The Dark Knight Rises" refer not only to Bruce's redemption, but to someone else's rise? Like an apparent rise from the dead?
It might almost be too much to have Harvey AND Ra's come back... would Ra's waste a Lazarus pit on Harv just to screw with the Detective, or would there be a larger plan?
Oh, I know... Nolan would never do THAT... I'm thinking like a comic geek.
Sure is hella fun, though.