Posted 02 August 2012 - 01:01 AM
Where do you save your downloaded media? If it's not in the folder structure of the application, or in other words stored on a second drive or different folder than the application, then no it won't delete your content.
Further, an installer, if written even with poor skills, should NEVER delete files not installed by itself. The installer for either VLC or RealPlayer only knows about the files it adds/installs and wouldn't know to remove your videos. It is possible for the uninstall to delete its own folder and all files left in them, including your videos, but that would be a silly move done by a poor installer and not something I would expect from either of the products mentioned.
If you have any doubts copy the videos to a new location until after your update.