Ok so skip all the putting little pieces together crap and lets get down to it.
Tobi = Obito because madara created zetsu a long time ago so he thats how he has all the info he does
So when madara died, zeztsu went on the carry madaras legacy out so, obito was being crushed zetsu saved him at the last second because obito was an uchiha and became his other half.
It literally makes easy sense that zetsu saved him at the last moment and took over madaras work
Lets look at what happened during and after Obito's last moments.
- Obito gets crushed by a huge bolder. Only his left arm and half of his face is not crushed.
- Obito is so convinced he's gonna die that he gives his only usable eye to Kakashi.
- Rin, a medical ninja, is so confident that Obito's gonna die that she performs the transplant.
- Kakashi is convinced of this as well and accepts the eye transplant.
- More bolders fall on Obito and crushes him even more.
- Kakashi passes out and Minato teleports to their location and kills all the enemies.
- Kakashi wakes up and Minato says he's sorry for not arriving in time.
Would Minato really leave Obito's body there without confirming that he's dead? Minato was able to kill all the enemies that remained. Which means that it wasn't like Minato didn't have time to confirm whether Obito might still be alive so he can teleport him to the hospital. Plus, Minato seemed like he had some sensory skills thats similar to what Tobirama had so I'm sure he could have just used that skill to check, if Minato was too lazy to check properly or something.
Also, villages will go out of their way to retrieve/destroy the bodies of missing shinobi's. Whether they are dead or alive, it doesn't matter. This would count even more in Obito's case, seeing that he possesses a Doujutsu Kekkei Genkai. What evidence is there that Obito was an exception to this? Did Konaha forget about Obito? Certainly not, because they celebrated him as a hero by carving his name on a monument.
I just reread this whole flashback and there truly is nothing that even slightly implies that Obito survived or that anyone in the Manga had any doubt about his death at any time. So, both Obito and this theory were crushed to death by the same boulder.