In an article published shortly after the "Better Call Saul" series finale premiered, co-creator Peter Gould was asked about how they landed on Kim's departure from Jimmy's prison as the final shot. Gould replied, "I spent a lot of time trying to decide whether to end in the interview room scene, with the two of them leaning against the wall, or to end with her leaving the prison."
For Gould, leaving them against the wall felt incomplete, and he said, “And it felt more honest to have her leave the prison because, of course, she does have to leave.” This closing also lets the audience wonder whether or not she’ll be back.
Gould also mentioned that at one point Kim was going to replicate the finger gun gesture Jimmy makes as she departs. However, this idea was nixed due to the erroneous impression it might give that Kim would return to scamming, and they ultimately decided to go a different route, landing on a series ending that felt right.