One of your responsibilities as playwright is to deliver a satisfying end to the play. You don’t necessarily have to write a happy ending or even an ending audiences would have wanted. You need an ending that seems truthful, plausible (given the circumstances), and, in retrospect, maybe even inevitable.
Use the following tips to build to and execute a satisfying ending:
Make the obstacles tougher and tougher. Be sure the setbacks your protagonist has to deal with are not easy and that they get tougher as the story progresses.
Create a cause and effect structure. Each moment and scene should lead to the next. (Although they happen in life, random events and particularly convenient coincidences aren’t dramatically satisfying in plays.)
Create a climactic moment that brings together your protagonist and antagonist in one final showdown. The entire play builds toward this moment when the protagonist meets his fate and the story line, if not the play, is concluded.
Come to the earned conclusion. The conclusion should be justified by the events that came before. An earned conclusion is a relevant and plausible ending that’s appropriate to the story you’re telling.
Avoid cheat endings. The deus ex machina ending involves a person or thing that appears suddenly and out of nowhere to provide a contrived and convenient solution to the problem of the play. Audiences don’t like this “cheat.” They expect the protagonist to find (or not find) her own way out of the situation.
Tie up loose ends in the resolution. The resolution, which comes just before the curtain falls, provides the opportunity for the audience to see the landscape in the world of the play after the climactic storm, big or small. This is where you should tie up any unresolved strands of the story.