Are you sure it was the real system temp folder the one you were looking into? By default it's C:\Windows\Temp, but to be sure, or for those customizing it to be something else, fire up a cmd.exe and do:
The .msi does definitely get extracted there. Sometime inside an additional subdir, with a random name.
Best bet: Run the official installer, and let it show that "win7 no longer a supported os" warning dialog. Without closing the dialog (so that the installer is still in memory, along with the extracted files including the .msi), do a full search on all of your local drives / partition, for "*msi" or "*intuit*.msi" or "*tax*.msi" (can't remember the exact name, but I may have mentioned it in my original reply?).
Or feel free to contact me at my userid followed by at geeemaaaail and the rest.