Yes, it will be sad. He's had a long career and written some great pieces of music. A legend that will be missed, for sure. But hopefully the progress of his disease slows down and gives him a few more years without sliding any deeper into forgetfulness.
I knew he was a Beach Boy for a while, when Brian Wilson stopped touring, but had not known he was also one of the Champs, after they had their only big hit "Tequila", way back then.
We did a tour recently through Colorado, Utah, and Nevada, and they played his "Wichita Lineman" as the bus rolled along the long stretches of desert road. Most suitable.