It's always kinda a balancing act. The Voices thing is a really good one on Arx, picking out people who are empowered with all the Head Honcho's authority ad spreading the workload around. But I really don't agree with people who say that faction leadership should always be NPCs. I get that it can be hard to find a player who can step up, but "NPC only" except for antagonists is always a call I'm iffy on. (Easier in a roster game, so the sphere leadership doesn't change every couple weeks.)
IC relationships, that can be another tricky one. I won't try and say there's a hard and fast rule for how much someone should be able to ghost on their IC significant other before the other player decides they're done for OOC reasons. Relationship RP is a big part of the draw for a lot of people, and someone who isn't getting that from their RP partner shouldn't be expected to stick with a ghost for the sake of the PCs.
Dependent PCs... okay, I really, really rarely do those myself. I need a HUGE amount of trust if I'm going to make one of my PCs that intimately tied to another PC, if I'm not planning to ditch the character if the other PC goes. The only thing I can say is to NOT do what one modWoD storyteller did, which was slate a ghoul to be executed because her regnant was gone for so long that she declared him IC absent instead of just away doing stuff.