Getting past the individual situation here it does raise some interesting questions about what ownership people have over information they submit for the good of others. If Quora restored all his answers against his will I don't think I'd object to that to be honest.
Put it in physical terms. If I volunteer to build homes in a third world country do I have the right to then tear those homes down if I become disenchanted with the organization I volunteered for? My answer to that question would be No and that's why I don't think he shouldn't have taken down the answers.
If the info was used just to benefit Quora that might be different but the fact that they benefit the whole of the community changes things IMHO