It should definitely not be possible for a plugin host to delete a plugin- since plugins may be used by many different hosts. A VST2 or VST3 plugin may be compatible with a host, but it does generally not belong to a single host (there are exceptions). Plugins are separately managed files at operating system level - often with their own installers.
I’m not currently running Cubase on MacOS, so I can’t help with current experience, but there seem to be quite a number of places, where one can find the location of VST2 and VST3 plugins on MacOS.