The stuff that you might, possibly, maybe have to re-download is only the stuff from DAZ that has been updated to the new DUF/DSON format.
I doubt it will be anything from Rendo.
4.5 only uninstalls what it installed itself, that’s basically the ‘Starter Essentials’ and its built-in content.
Items you installed separately, (even other DAZ products) are not touched by the installer.
(Though its always good to have the original installers backed up somewhere)