It worked. When I stopped the install in tskmgr, I believe that it exited nicely... (after a few mins) but I may have forced it close a second time.
ANYWAY, I rebooted - and there is the QB 2018 icon on my desktop. I did not click it, and instead restarted the install from scratch. It may have elected to 'repair' the install. I just accepted whatever popped on the screen. (Not sure if the QB icon would have worked or not.)
One other interesting tidbot - for me - when I tried opening my old 2015 QB file, it gave me an error. I tried opening it a second time, and it converted it / etc. So be prepared to open a file twice for the first time.