Google, and other search engines, will spider Nabble regularly. The next time this happens the spider will discover that the topics no longer exist and they will be removed from their database. When the next trawl of Nabble will take place is difficult to predict. It could easily be several weeks and maybe more. There is not much, if anything, you can do to affect this cycle of spidering a site.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.