If I archive or trash a message, and then someone replies to it later, will it show up in my Inbox?

Yes, if someone replies to a message you archived or trashed, that message appears in your Inbox as a conversation, with all previous content. If you applied a label to the archived message, the label will appear in your Inbox.

If the message was permanently deleted from the Trash, you’ll see an option at the bottom of the message to view the deleted messages in the conversation. However, the message won’t have the original label you applied to it.