In the play Stop Kiss by Diana Son, why do you think the playwright decided to stop the play with the kiss?

Diana Son's play Stop Kiss revolves around two women, Sara and Callie, living in NYC, who are assaulted after kissing on the street. The playwright's decisions about the chronology of the show cause it to literally "revolve" around the incident of the assault—we do not see the assault happen in the play itself. Rather, the play alternates between the time before the incident, when the two women meet and get to know each other, and the time after the incident, when Sara is in a coma and Callie (along with Sara's ex Peter) helps nurse her back to health.
The effect of having the play "revolve" around this incident chronologically is to enhance how it revolves around the incident thematically as well. The assault is a result of Sara and Callie's first kiss. Sara's coma is a result of the assault. And ultimately, it is through the aftermath of the assault (Sara's coma, the trauma of it, the physical act of caretaking, and the deepening and rupturing of various relationships) that Sara and Callie are able to choose each other more fully and go forward in their relationship. The "before" and "after" sections being told in an interwoven format allow them to inform each other and to reveal information about the past in ways that complicate or explicate the present.
These are the two final scenes of the play:
First, in the "after" storyline, Callie comes to the hospital and struggles to help Sara get dressed, and when they finally manage to do it together, she asks Sara to "Choose me."
Second (the final scene of the play), in the "before" storyline, Callie and Sara leave a bar at 4 a.m., and while walking down the street and asking each other silly questions, Callie kisses Sara. They fumble to kiss a second time, and the play ends with Callie saying "Try again," and the two of them kissing.
The effect of juxtaposing the storylines at this moment is to show a certain symmetry between this beginning of their romantic relationship and their decision, after going through this trauma together, to choose each other and continue that relationship. The fumbled struggle is mirrored in the two moments, as is Callie's invitation to Sara to choose, to try again.
In allowing the kiss to "linger" in a way at the end of the play, having the play end on that moment in its implication of coming violence but not allowing that violence to be seen, Son places the emphasis on the two women and their relationship. It allows that relationship to have the last word, while also acknowledging (in an unspoken way) the enormity of the violence, the way it looms over the play and over their relationship in a way that can't be ignored. One could say that the kiss was the catalyst for the relationship, or one could say the assault was. To choose to focus on the kiss doesn't erase the violence, but it frames and elevates the connection and resilience of the women, rather than the violence against them.