This has never happened to me (fortunately) but in case of emergency I would use
ninjastic.space from TryNinja.
From there you can get your deleted/edited/destroyed text back 1:1
That's only if you've posted it somewhere on this forum, but what if someone hasn't posted it and he or she accidentally deletes all the text? Looks like the OP's situation is exactly the same as what I'm asking you this because he probably hasn't posted it yet but the text was deleted by mistake.
If the OP copied it from somewhere else
[notepad or something] then he probably still has the data in the clipboard to paste again on the whiteboard, but if he manually writes it on the whiteboard then he just has to rewrite the whole set of text to post it. One suggestion to the OP that I found helpful, always take advantage of the preview button function so you can minimize errors
[missing text on the whiteboard due to accidental deletion] because if that happens then you just have to copy it from the draft.