Gmail, final filter: move messages back to inbox and keep them there

I receive a mail from mailing lists where each list is assigned its own label and removed from the inbox. However, I do want messages to which I respond returned to the inbox and then kept there.

1. Using as the last filter in:sent has:userlabels, how can I move threads back into the inbox?
2. How do I prevent responses from removing the thread from the inbox?