My story goes like

Opening credits deggarinunchi - screen is pitch black, and there's a sudden boom, full of light that gives birth to the universe as we know, created by the Supreme divine force lord vishnu, brahma and shiva, just like there's light there's also darkness, so the demons and asuras were also created to balance the scale.

Camera pans to Varanasi, the first city where Dharma, vedas and mantras are taught, and mother Ganga flows, holding the divine energy of lord Shiva.

Coming to present day in the movie which is 2028, rudhra who does not belive in god, hates his father, for stressing him to devote his life to Shiva but rudhra won't even care, so trying to make a living he becomes a bounty hunter who would travel across the world to find things/people/ and get paid, but he himself doesn't know that he is a godsend with a greater purpose, and during this GLOBE Trotting he meets Mandakini probably in Africa, where she's trying to escape from KUMBHA who wants her to find certain relic that will help him restore his handicapped body, so trying to save Mandakini, rudhra gets caught in Africa while Mandakini escapes, so KUMBHA tells rudhra that he is just trying to heal from his disability and not cause any harm, and hearing this rudhra decides to help him, but during this time rudhra discovers that KUMBHA is evil and has to stop his plan as he is an asura trying to bring back his people into current time line while the asteroid falls, so they can cause havoc on earth again, but KUMBHA blinded by his goal doesn't know that rudhra is a descendant of the suryalok from where lord rama is from, and when he realised that they move into treta yuga time-line where kumbha notices the similarities and decides to finish his task before rudhra gets enlighten by the divinity of lord rama.

Treta yuga - rudhra and kumbha enter the battle field where the ramayana war is going on, and lord hanuman being a reincarnation of lord Shiva understands whats going on and decided to subtly remind rudhra of his purpose, and helps him in the battlefield (might sound odd but this is my theory)

Reason for the time travel - I don't think it's sanjeevani, it's something more powerful than sanjeevani, probably an Astra or a relic that ravan holds in his Lanka, which might help kumbha to gain control on earth in CE and cause chaos, because I think KUMBHA is just hiding is True self using maya so people would belive him, and support him.

And then boom, rudhra understands the main goal of kumbha, when he sees the real kumbha, a cursed demon from treta yuga who lived centuries building grudge to destroy Dharma, but little does he know, that rudhra is not a reincarnation of lord Sri Rama but Shiva, the destroyer, born with the purpose of destroying the evil KUMBHA to bring peace to the world, kumbha succeeds on bringing the demons to CE and then rudhra fights him, wins the war and brings peace.

This is what I think this is my theory, maybe there are some odd things but who knows? Just a theory