A conversation between George and Slim at the end of Steinbeck's work could take different forms.
One of the most traditional approaches would be to continue the dialogue already there. When Slim finds George at the end of the book, he steadies George and tells him that he had no choice in what he did. This might be where a conversation could continue. George's tone could take a confessional form, similar to the tone he took in Chapter 3 when talking to Slim about what happened in Weed. George could express regret over what he did. Slim could provide counsel, suggesting that George did the right thing. This conversation could illuminate an emerging friendship between both men, adding a new dimension to the novella's theme of friendship.
Another approach would be for George to accept that there was no excuse for what he did. While Slim would argue the opposite, George could simply respond in suggesting that from traveling with someone, he is now forced to travel and live alone. This might prompt Slim to have to rethink what he said in Chapter 2 about how everyone is "damn scared of one another." Slim could realize that we might not be scared of one another, but rather scare of ourselves. George would be living proof of this revelation.