one shot from fu and the fight is pretty much over if he takes over deva path.
The chances of it hitting are low (remember, it travels in a straight line), it can be dodged easily. If it's dodged, Fu's body will be useless for minutes. More than enough time for Pain to kill him.
Assuming it does hit Deva path (that's a big assumption), Nagato can probably counter by deactivating Deva, then reactivating him (Nagato might have to have his other paths kill him then revive him before that). Hell, I'm not even sure Shintenshin would take Nagato's control of whatever path is hit away from him even if it were successful. Remember, they're just dead bodies, they don't have minds. Though I'm not quite sure what would happen if Shintenshin hit, whatever happens, Pain should be able to counter it.
Anyways, Pain would probably kill Fu and Torune long before Fu even gets to try Shintenshin. Especially if he has knowledge.