ᛞᚨᚱᚹᛟᚾᛞ: I don't like how there isn't a text buffer, so unless you've saved your post somewhere externally, kiss your original post goodbye.
If you're talking about the occasions when a reply you've posted never actually appears, even after several minutes and someone else having posted in the thread: As long as you're still in the same browser session (and you haven't closed too many other browser windows--including other post-edit windows--in the meantime), you should be able to go into the list of recently closed windows and find the right "Add new post" composition window (a little trial and error may be required if you've made several posts recently, since all these edit windows will have the same name); upon re-opening it, all your text should be resurrected, too. Worst-case, you may have to copy & paste it into a fresh post window to get it to actually post this time.
(Yes, this is a browser feature (in Firefox, and I assume most other modern browsers), not a forum one, but it's still the case that you don't automatically have to treat the "lost" post as irrecoverable just because it failed to actually post the first time.)
