Q. I really loved To Kill a Mockingbird, and Atticus Finch was my hero. Do I have to change all that in view of the publication of Go Set a Watchman?
A. Only if you want to.
If you don’t want to, there are several good reasons why you shouldn’t have to.
Reason One: Go Set a Watchman is not a sequel to To Kill a Mockingbird just because it takes place in a later decade. It was written before To Kill a Mockingbird, but wasn’t published until just now. If either version of Atticus Finch is to be regarded as the “real” one, the title should go to To Kill a Mockingbird Atticus (“Atticus Prime”, as the Star Trek fans would put it) rather than Go Set a Watchman Atticus (or “Reboot!Atticus”, to continue the Trek analogy), by right of prior publication.
Reason Two: Given that To Kill a Mockingbird and Go Set a Watchman, by virtue of their peculiar history, do not actually stand in a text-and-sequel, or even a text-and-prequel, relationship, but are separate books, then Atticus Prime and Reboot!Atticus can safely be regarded as distinct and separate characters who just happen to share a name and place of residence. (Again, science fiction readers already have a model to hand for dealing with things like this: two separate universes, parallel but different in some key respects. Not quite Spock-with-a-Beard territory, but similar.)
Reason Three: Go Set a Watchman, until recently, was never meant to be published at all. It was what is sometimes referred to as a “trunk novel” — that is, an early work that the writer, usually for good and sufficient reasons, has put away in a trunk (or a desk drawer, or a computer file in an increasingly-obsolete format), never to see the light of day.
Sometimes, however, a trunk novel does eventually get published. A writer may achieve sufficient popularity that it becomes a good bet that readers will buy even his or her old grocery lists, at which point somebody — maybe the author, but often the author’s literary heirs or executors — will decide to haul that manuscript out of obscurity and turn it loose on an unsuspecting public.
The reason for this, not surprisingly, is usually money.* Either the author needs it, or the heirs-or-executors want it, or both. If the author is dead, and the heirs-or-executors are nowhere in evidence, then the coin involved is likely to be scholarly reputation.
So, no. You don’t have to throw out your copy of To Kill a Mockingbird and consign Atticus Finch to the dustheap of abandoned role models unless you, personally, want to do that thing. Which is your decision to make, not mine, and if I have any position at all on this, it’s that every person has a right to their own reaction to a work of art.
*Because writers have this annoying tendency to starve if they can’t buy groceries. Go figure.