No, I don't think the wild yeast would have survived that. Do you think you're smelling sulfur? It's the most common off-flavor I've noticed with cider, and the Campden really amplifies it.
If you think it's sulfur, try stirring it gently with a bit of copper pipe next time you pull a pint. It works amazingly quickly. If that eliminates the sulfur, and it very well might, then it could be as easy as pushing it to a new keg with a bit of copper tube in the line.