They drop off the online table after whatever time period you specify (default 10 minutes). Threads cannot track them or update their activity time unless you are refreshing the page. So not sure what mod you're using. One of my mod used a pop-under window which refreshed every 9 mintues and updated their location - and my current Raidersoft mod updates a header (in an iframe) every 9 minutes to keep the table updated. But if the page isn't refreshing - they "drop off" the list after the specified time of inactivity. Even if they are in chat - threads isn't tied into the chat server in any way to know this.
