...
This has happened to me and I ended up leaving the topic to remain unmoderated. There is always a tendency that one could forget if your consciousness is not there.
And sometimes, I just notice it a few hours later, after several new comments below my OP.
By then, it's too late to delete / trash my topic since it would also trash the comments which were already left...
This should not be a big problem.
The program be written that posts which were made when the topic wasn't self moderated shouldn't be possible to be deleted. The ones which were made after the post became moderated can be deleted.
Previous comments shouldn't be affected.