What song would fit the ending of Romeo and Juliet when the Prince says the final words?

If I were directing the play, the main consideration in selecting a final song, perhaps to be played as the audience was leaving the auditorium, would be the staging of the play itself. If the play were being staged in traditional Renaissance costume and aiming at authenticity to the original, I would search for period-appropriate music. Since the two leading characters have recently died at the play's end, I would choose a requiem, a musical composition that was part of the requiem mass or funeral service in a church. 

Perhaps the most distinguished English church musician of the period was Thomas Tallis. A recent release by the Tallis Scholars, a superb choral group, called "Requiem" contains several of their performances of Requiem Masses by Tallis and other composers of the period. This would be appropriate to the mood and period of the play, as it would resemble what the characters in the play and members of the audience would have heard at an actual funeral.