In light of new evidence, we have discovered that the Gold Pirates were present at Roger's execution. So, what exonerated them from capture/being hanged? Certainly, without Roger to protect them, they were at the mercy of the World Government. None of them, save for Whitebeard, were any more than kids back then, and surely would have been caught.
So here's what I think. Roger knew that his increasing fame across the world meant that more and more people knew the members of Roger's crew, and when they went off to make their own crews, they would be plagued by marines, bounty hunters, and everything else. Not to mention their association with the Pirate King would also have an effect on their relationship with various people across the world.
So in order to prevent any kind of problems, Roger set up a deal with the Gorosei: In exchange for total Amnesty of his crew, Roger would surrender himself. Having achieved his dream of being Pirate King and discovering the one true history and reaching Raftel, Roger had no real reason to keep on living. It was time for him to pass the torch to a younger generation, the generation of Shanks, Buggy, and others.
Once his surrender was final, the crew became normal citizens, free to go about beginning their own crews if they so desired. Others could become regular citizens, such as possibly Crocus, Kureha, and others.
If you don't agree, how do you think the Gold Pirates were exonerated?