But, if this WD season is about "can you come back", wouldn't Rick be willing to negotiate in some way? It's one thing to kill someone in the moment of self defense, it's completely different to execute someone for their past crimes - particularly if they are remorseful. If carol had shown any remorse when she was out with Rick, he may not have banished her, but she was heartless.
No, if Rick wouldn't let Carol come back to the prison, there's no way he would let in the Governor. He doesn't bring in anybody he deems to be a threat, hence his system of three questions to hopefully weed out the psychos. We know the Governor is crazy, has a personal vendetta against the prison and everybody there, and has already attacked the place twice. Even if Philip came walking up like, "I feel really bad about all of that, but I want to negotiate a truce!" do you think Rick or any of them could ever believe that? He's murdered some people from their group and then tried to kill them all, knowing full well Rick had children there. If Rick told Carol he didn't want her there because she was possibly
a threat to Judy and Carl, there's just no possible way he would even consider letting the Governor waltz in there after his mass-murdering spree, whether he felt guilty or not. And even besides Rick, Daryl or Michonne would probably kill the Governor as soon as they saw him, not to mention that none of the former Woodbury residents would want him around, either.