First, this is not a Tobi is obito thread. I don't think that. Even tho the idea of a vengeful uchiha who couldn't contend with Kakashi also his best friend/rival briga an almost sentimental feeling to my heart, I believe obito died, unless his eye activated because his life was on the line and he became fazed hia body out to sirvive and dosnt know it until a zetsu or madara came along to how him, but never mind that.
What I do think is a little complicated but not entirely far fetched.
Tobi is madaras brother, either by edo or some type of power up that will be made up.
Why I think this.
1. The story of madaras brother believing in his goal so much that he gave him his eyes voluntarily has not been proven a lie. If this is true it would match up to tobis obsessive loyalty to madaras moon eye plan and the eventual reviving of the true madara, not Kabuto and oros edo.
2. Even how tobi told the story of madaras history with the clan and leaving the village reminds me of how sauske talks about itachi. And we all know how kishis big deal is the previous generations being relived through the next. (sosp sons =madara and hiro) (hiro and madara = naruto and sauske) (oro, jiraya, tsunade = sauske, naruto, sakura).
3. Tobi has shown he collects eyes, he also showed a vast knowledge of the special techniques passed down through blood, I.e. his battle with danzou and his body guards. It's not impossible that he knew of obitos family line and special techniques, especially since he was a uchiha. Why wouldn't he collect that eye in the middle of the war.
Also with this I'm not sure but I'm pretty sure diedara was featured in the Kakahi arc as a rock nin fighting the 4th. This jut connects random dots to tobis knowledge of powerful shinobi to recrute, of course I could be wrong.
4. Also madara seems pretty twisted and has shown to know as much if not more about edo as the second hokage who made the technique, I don't think it's that far fetch that he would dig up his brothers body and revive him, since he's the only uchiha he had left to trust.
And with this, I've never really seen tobi get tired or "run low on chakra" might be his uchiha blood letting him slip between space and time unfazed but even sauske, kishis poster uchiha boy got wrecked from usin his eternal eyes. But edo s do not get tired, they get frustrated, they complete whatever mission they are suppose to, but they never stop.
Oh and finally hea the only character from the past that kishi hasn't shown, and he loves that kind of shit, I mean he found a way all though premature, to Show the first and second, and he even managed to close loose ends with the 4th and narutos mom. This is his big surprise and I just put it on blast #boom.
But if you find credible flaws in my theory I.e. chapters that show tobi tired, diedara not being in the arc etc please let me know.