It is now pretty well documented that the last thing Alzheimer's is able to take from people is their musical memory.  For example, someone with a CD of songs of the 40s visited a seniors facility and played some of the old songs of that era.  A resident in his 80s who had not spoken in a couple of years suddenly started to sing along with the recording.

As for Glen, one of the major pluses of the business he was in (although he was all about the music not the business) is that he will live if not forever at least as long as people still listen to English language popular songs.