I thought about this as well, Obito has to die but we don't know whats going to happen with his eyes specially Madara's Rinnegan.
My theory is that after reviving Naruto, Obito will die, and destroy the Rinnegan ( Madara's overpowered as it is so maybe Kishi will let them destroy it) I can't really see Obito leaving his dimension at this point, it would be retarded if he went back weak and just "handed" Madara his other eye.
Obitos Sharingan is very unique and probably my favourite! Obito was beast with just one Sharingan imagine what the true power of Kamui is capable of. It would be sick if Kakashi had both of them instead of leaving their combined potential a mystery since both eyes still exist, it'd be kind of bland if Obito just died with his Sharingan and they just left him with it imo.
Either that or Obito will pull a Itachi and destroy it like Itachi did with Shisui's lol or Obito lives after the war and becomes a valuable member of the leaf XD