Comments Etiquette question:

I think you can just stop when you have nothing more to say. Like if you were on the phone, if both people keep saying goodbye over and over and waiting for the other one to hang up first, you will be on the phone forever.

I don't think it's rude not to reply if you have nothing more to say. Sometimes it's a case where others have already said what you are thinking so there's no point in parroting the other person/people.

Sometimes I just toss an idea out there and let the chips fall where they will. If people want to discuss, great. If not, that's ok too. The thread will be buried.

It is never goodbye on these sites. There is a whole reason as to why discussions still start years after the original post was made. Message boards are just there to add new responses to threads that may all ready be there.