[quote=@The Fox Without]
[@Double]

Gotta a few background ideas, but need to know, do you think of Gannondorf as the type to take prisoners, or more the kill shortly after interrogation type. Trying to decide between hiding in plain sight, escaped prisoner, or recently returning after being shipwrecked.
 
Apologies for badgering you with questions. 
[/quote]

Depends on the threat level, really. That, and how useful they might be to him in the future. He killed Impa and Darunia because of their prior reputations for being skilled warriors and capable fighters (their loyalty to Hyrule couldn't be broken either). He turned Nabooru back into the Iron Knuckle because he figured having a big iron tank for a general would be useful, that and her history for being under his control made it feasible enough to go through with. He kept Saria and Ruto alive, because, honestly, they aren't fighters in the slightest. They have Sage powers, sure, but the game shows that both of them are pretty useless in a fight, so Ganondorf didn't see any reason to kill them straight away.