Crap. I have to retype everything because I accidentally closed the page. 0_0. Alright, here goes:
Nagato's shared vision counters Madara's perception. He can have summons in the air, invisible, and such to tell him when Madara's swinging. So he'll just have to focus on evading and countering. The second Madara goes for the swing, Nagato will know and he'll be able to propel himself away/up with Asura rockets and hit the sword with Shinra Tensei to cause Susanoo to lose balance and topple over. And the surrounding impact doesn't do much because Nagato can repel it too.
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is Nagato's Shinra Tensei when he's at near-zero chakra levels. I'm more than certain that Nagato can counter a sword swing head on. But, as shown above, he doesn't need to when he just has to avoid and hit Susanoo whilst its in mid-sword swing to cause it to lose balance. Pains Shinra Tensei <<<<<< Nagato's.
And yeah, Nagato can sill survive two swords due to shared vision alerting him when Madara swings, thus allowing him to dodge one swing and counter the other with a Shinra Tensei. Once Susanoo's knocked over, Madara's done for. And its not a far stretch to say Asura propelled Nagato
= V1 A's speed, or is at least near it. To win, Nagato has to evade and get behind Susanoo to topple it, or evade and topple Susanoo right then and there.