He mentioned that there was a pop-up with a progress bar that seemed to hang about 3/4 of the way through, but when I went over I think there was a similar pop-up for the removal that completed. Can't say that anything became stuck; only that after the running the installer after AA 11 was removed (and system rebooted) there was no Lavasoft folder on the Start menu. He is no longer being prompted for the AA 12 upgrade, but I guess that's because AA isn't on his computer any more.
My father-in-law got the AA 12 upgrade prompt on his Win10 system, so I went over to help him through the steps. The installer first removed AA 11, but after rebooting we basically had a Win10 box without any Lavasoft products installed (not in Start Menu). We ran the installer again, but nothing happens. Doesn't matter how many times we run the installer.