Well the fact that Dyne realised the error of his ways and chucked himself off a cliff sort of rules that one out…
yeah the rock he jumped off looked pretty high up! but he could just come back with a new gun arm, 2 gun legs, a gun head and a gun body!
Death is normally a fatal thing to occur.
In saying that, I managed to resurrect Aeris, Sephiroth and Rufus in my FF7 sequel I wrote, so anything’s possible.
Personally, if I were Square, I’d do something different with Advent Children. Having Cloud as a loner vigilante sounds like a cool idea: Keeping his promise to Aeris. No resurrection of Sephiroth (perhaps just another clone), no resurrection of Aeris (maybe a spirit, or a new Cetra, or something), no resurrection of Rufus (the dude was blasted quite heavily), and no resurrection of Dyne (no matter how many bad ass cyborg implants you give him.)
Juz my opinion.