If they're all restricted to using the Rinnegan features they've shown only, then Nagato wins. I only read the first page and am guessing most everyone does not know the circumstances of the fight. As for how he mends with Gai, the Rinnegan provides nothing that's going to stop a direct hit from Night Gai, and assuming he hasn't activated it yet, Nagato may be able to summon his lizard and retreat into an invisible state and hope the explosion does not reach him. Another possible route would be summoning the King Of Hell and depending on whether or not Gai gets sucked in without a collision occuring, he may end it right there.