I too, think Fred is fine and wandering out there. I don't think the Volturi would have searched for him after the events of Eclipse. I would like to think Edward went looking for him, but I'm not sure he would have, nor even if he could have found him. I have heaps of questions about exactly who his talent works on. I think SM says in the guide that it's more physical than mental, and that makes me wonder if it would work on Bella.
I think Fred's smart enough to know the rules anyway. Bree told him to "hunt smart" and as he has the ability to go unnoticed, he'd probably know instinctively that he needs to keep a low profile. I think he'd keep to the nomadic life quite well, whether he knows about the Volturi or not. Should he know about the Volturi, I think he'd be suspicious of them. I don't think he'd witness for them, especially after the events of Eclipse. He'd be too suspicious of their motives. After all, Riley's turned out to be suspect. Why not these new vampires, who are claiming that they are the benevolent rulers of the vampires?
I do hope he gets to meet the Cullens one day, though.