HOW TO CONCLUDE A TRILOGY

I've sent the publisher my final manuscript of book-2 in the BLENDING TIME trilogy: THE FIRES OF NEW SUN. Now I must finish the trilogy with book-3, to be finished by year's end. Questions to self: Do I have a 'happy' ending? It's a dystopia, so the ending cannot be a joyous, doing-cartwheels ending. Do our heroes (Jaym, Reya, and D'Shay) settle down, or go off to another another struggle in their dysfunctional world? Ah, so many ways a writer can go. Any reader tips welcome! (No title yet for bk-3).