When Mr Krupp dies of old age, George and Harold would sing No One Mourns The Wicked just like Ding Dong The Witch is Dead until they realize that Captain Underpants died with him. Not to mention, he had a sad, pathetic life with nothing to his name (not his hypnotized name, his real name) but a failure of a school principal. In which case, it becomes just like how Glinda was singing it, secretly going against the theme of the song in the first place
After all
The wicked's lives are lonely
The wicked cry alone
It just shows when you're wicked
You're left only
On your own











