This is not about Cubase but about the Steinberg Download Assistant which has no appropriate category in this forum.
When downloading a file that already exists -but with a different checksum (e.g. because it got corrupted) - it will be downloaded again. The newly downloaded file will have a name where an index is appended, to not overwrite the old file. So far so good.
However, when deleting or installing (still with the Download Assistant), the old (corrupt) file will be deleted or installed, respectively.
Best behavior upon detection of a corrupt file would be to ask if it should be deleted or moved elsewhere. Then, there can be no confusion about renamed files for either the Download Assistant nor the user who may manually inspect the download directory.
Version 1.35.0 on Windows 10