I was thinking this recently but Paige is not the only tragic character on the show
I get why the actress wasn't available for the last season but I can think of 4 other characters that really were sad characters.
There's Nathan although that's probably self-imposed as he admitted to Sheldon about not bothering to look for work.
There's the librarian, Ms. Hutchins, who likely stayed depressed and single.
There's Billy Sparks who likely didn't ever graduate middle school.
There's June who admitted to Connie that she has no friends.