I dunno, I thought the ending to FFT was pretty bleak. In fact, I think if Versus is going for a Shakespearean tragedy feel, they should probably aim for or above FFT proportions.
Though generally speaking, Crisis Core probably is the only FF that is straight up tragedy.
Or, they could go the route where everyone dies save for the main hero (I guess Noctis in this case), but in the end, he learns that he had been fighting for the "wrong side" so to speak, and all his comrade's deaths were in vain. To me, ends where the characters actions amount to nothing are the most dark/dramatic/depressing.