Thanks for the additional replies.
There are definitely far too many topics to manually revert the revisions. It looks like the lesser of the evil options will be to open all of the deleted topics and manually click the un-delete button (which unfortunately is located at the end of the variable length original post, so requires scrolling to search for the end of each topic and then expanding the … menu to reveal the un-delete button).
I’m sure it’s quite a process behind the scenes. But I really don’t understand why a UI bulk un-delete action couldn’t be added if there is already bulk deletion implemented plus the listings of the deleted topics that are already available with a bulk selector.