Reinvention is the only way for a popstar to stay relevant because we live in a postmodern world where everyone has ADHD (according to a friend on twitter). We don't have the attention span required to put up with a person remaining the same ol' person all their lives. You need to continually come up with new concepts to keep millennials entertained.
Artists who have figured this out:
I will focus on EXO and Rihanna because they are the two most exciting musical acts right now, in the East and West, respectively..