Re : Accidentally deleted a topic!!!
In 1.8 (at least), changing pic seems like a simple business in Admin topics...just editing the topic. Maybe you missed something there, or you looked for something too complicated.
About the articles, 1.8 shows a "Remove" link and a "Remove with articles", if you selected the latter I doubt there would be a way to recover.
I tested this in 1.7 too, and could see you would have been unfortunate if you use that version 
you could hopefully find a MySQL trick, but Tiki itself can't help there.
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