Most forums and many websites (like gmail) are able to save your post in a cookie as you type. If you navigate away by mistake, the post will be waiting for you if you go right back.
Does the billion dollar forum have that feature? I got so used to it I forgot this forum is so old... :/
Did you go back to the browser page or refresh (F5)?
Well, if you refresh, unfortunately you will have to start all over again, unless you have clicked on the "Preview" button at some point.
If you simply clicked the back arrow (or the key/mouse combination for that purpose), simply click the forward arrow to return to where you were.
Now, perhaps there is no need for new software for the forum, perhaps a small patch could resolve the issue.
@PowerGlove is it possible?