I'm really half-and-half on this, personally. On the one hand, I agree to some extent. But on the other, this is Star Wars. There's a certain built-in universal precedent for much of this. The unnatural, arcane power of the dark side provides for Maul, with such extreme examples as Darths Andeddu, Scion, and Krayt proving that Maul is but one in a lineage of death-defying Sith. And in the case of Trench, the modern galaxy is vastly superior in technology, with an astounding level of cybernetic prosthesis that could repair nearly any bodily damage if applied in sufficient time. As for Starkiller, he is dead. He never came back. The character in TFUII is a clone, cursed with imperfect memory flashes from his progenitor. That alone creates an interesting story in its own regard, with the ability to question the perception of identity based on what determines self: memories or actions? That said, Tamson is an obvious candidate for not returning. No amount of cybernetics can return life to...chum. And Mara succumbed to poison spread throughout her bloodstream. To even consider bringing her back, they would have to remove the toxins from her blood, and reverse the damage done to affected tissue, not to mention the deterioration of synapses. Steela suffered impact trauma the likes of which would have led to massive internal damage and brain trauma, that while theoretically treatable by Star Wars standards, wasn't an option so far out from sophisticated medical facilities. And I'm honestly in favor of Gregor not returning; while Katarn-class armor is ridiculously resilient, that was a hell of an explosion. If Fi incurred brain trauma from an indirect shelling in True Colors, it's a bit much to think Gregor's going to walk away from a direct explosion of that caliber.