Thanks a lot, this tool fixed my issues with missing *.msi. The installer tries to deinstall old versions, but failed to do so: There were still residues of old installations (Desktop + Diagnose) , but no matching (un)installation msi left.
After using the tool to cleanly deinstall these remains, I also had to manually remove the Viveport Desktop Service using SC.exe in the commandline as administrator (sc delete ViveportDesktopService).
Hope this helps someone :)