if indiana jones had stayed home in Raiders, everything would've played out the same. the Nazis would've still got the necklace, still found the map room, still found the Ark and still got melted.
The Ark was a McGuffin.
The story was more about Indy's journey through searching for the Ark, and his reconnection with Marion.
The culmination of that journey was in Indy's choice between destroying the Ark or also seeing what was inside of it.
Like Belloq, he too could not resist the mystery, even though it meant surrendering both himself and Marion to the Nazis and whatever fate they had in store.
Now, the Ark was a manifestation of the Will of God, and of course it was practically a given that it would choose the side of good.
Being a Divine object, it could also be said that it saw fit that Good would triumph over Evil no matter what either side did.
( Its why it would not allow itself to be abused by the Nazi's, but would allow itself to be sealed up again and stored away by the Americans. At least they understood there were some things that Mankind were not meant to know....)
The lure of the mystery was always going to be Indy's downfall, and it was the source of his constant dire plights, but his good sense ( usually at the last moment) wins out and saves him.
In the Last Crusade this is apparent as he tries to reach for the Grail, the lure of it enthralling him. Its only the steadiness of his father telling him to forgo the Grail at that penultimate moment does Indy realize the futility of dealing with the Supernatural will.
Its a lesson he struggles with in Raiders, Temple of Doom and Last Crusade.
So while the outcome of bringing the Ark back into the world, was more or less a given--Indy's journey through these adventures was not.
