A Sales Starter or Professional messages conversation with a visitor on your website can be closed in two ways:
1. You, the HubSpot user, manually close the conversation by clicking the Close button in the upper right corner.
2. If neither you nor the visitor you're chatting with have sent messages for 30 minutes, then the chat will be closed.
Once a chat has been closed for either of the above two reasons, it will be reopend if the visitor sends another chat during their same session on your website.