I think I may have had that problem before once or twice, I just hit back on my browser and my text was still there in the text box so I just copied it and pasted it after refreshing the page or relogging in (can't remember what I needed to do exactly). Make sure you check the remember me box when you login if you didn't.
As far as the script to check if someone is typing, that would consume a lot more resources on the web server from sending the notification as well as all the users. It would be possible and not a whole lot more bandwidth but I don't know if this site is limited on that or not. I'm going to assume it's unlimited, but it still doesn't seem necessary as it would reduce page loading times slightly, even though you wouldn't notice it too much it would add up.