I believe deaf people should strive to assimilate in the hearing society, but they can also have their own group of friends that are reliant on ASL. I think this really depends on where this person is. In a densely populated area it is likely they will be able to find others like them and that is great, but in rural areas it is far less likely. I wouldn't suggest anyone cut themselves off from society unless they make that choice knowing what it is like to be alone most of the time.
There are not values that are unique in terms of lifestyle to deafness that would make it constitute a culture. Deafness is a condition which strikes people in a variety of cultures and there are no unique values or practices which are universal or even semi-universal to deaf individuals. The idea that those who assimilate into hearing society are "traitors" is to presume that only a limited number of the deaf are "real" and other people with the impairment are "fake".
ASL is very valuable to the deaf community, and the hearing community would be well served to learn ASL. However, the deaf community is not much different from a community of non-native English speakers. If they cannot speak the local language, they will be limited in their communication to only other people that speak ASL. The deaf community should strive to assimilate in the same way that immigrant communities strive to assimilate.
Being deaf is hard enough without trying to assimilate. While it is true in theory that there are benefits to assimilating into a larger society, in practice it is often the assimilated who has to do with certain sacrifices. It would be foolish for the deaf to turn their back on a supportive community which understands their needs.