Madara had to have given the eye he stole from Kakashi back to Obito. Why? who knows.
Now I don't think Obito has a deathwish in his heart. Im pretty sure theyre stemming on the fact that Madara placed a seal on Obito's heart that prevented him deviating from "The Mission." I believe they said Obito got into that fight with Kakashi in the other realm and intentionally allowed him to use his Chidori and pierce him through the heart. That removed the seal and Helped Obito become the Juubi Jinchuuriki.
Naruto apparently can heal anyone with his 6th Sage Senjutsu. I believe hes simply unable to repair his heart to make Obito feel human again. With this reality, he says He'll die to help save the world.
I think Sasuke has the power to get back, He just doesn't know how.
Also Obito should get a Susanoo. But lowkey, I think certain fans will agree with me, But i believe Obito deserves the Rinnegan. Unless someone is willing to argue that you need EMS First. Hes been cultivated with Hashirama's Cell since his accident and now he finally has both of his eyes again.
The true question is, What is Kakashi's role?