I actually don't see how he's going to see Rumple from 4 km away, knowing they are on the Central Park, NYC - which's full of trees, buildings and such, blocking the vision. That, of course, not considering the other people walking around the street, of course. Rumple has already lived in NYC, and would know how to use the environment to grant himself an advantage. I mean, there is a very high chance Captain will not even realize he's in a fight with the Dark One until it's too late.
Also, I didn't get why he could not see his future, why they are "locked", it didn't make much sense to me - but it could if properly explaneid.
That is, it will bring a lot of issues up. If Rumple could not see his future up to that point, there is a 100% chance he would try and teleport to another dimension as soon as the fight started. He dislikes facing the unknown, and doing that head on would be extremely out of character for Rumple. He's intelligent, you know.
With that, he would be out of range for Captain and his summons. And from there, he could very likely use BFR and trap Captain into a realm from which he could not escape. Strategy and such.
And about the atomizing thing, it would get us the very same result. By atomizing Rumple, Captain would grant him a strategic retreat, because the Dark One's Vault is in another realm. After his body rebuilt there, he would not be crazy to go head on and face Captain again, and would most likely use his powers from the safety of being in another reality to end the fight - by BFRing the boy to another realm, for example.