True, Guts and Casca wouldn't have survived, they were meant to die there, if it weren't for Skull Knight they would'veAn apostle has been branded in the series, but he's not a normal apostle and it's a very specific case, unlike anything else. I'm talking about the beherit apostle of course, who sacrificed the "world around him" and who sports the brand on his tongue.
Beyond that particular case, the scenarios you list above can't really work because that's not how beherits or sacrificial ceremonies occur. People who become apostles don't do so by random chance. It's all preordained through causality. That's why Guts can't just use the beherit to summon the God Hand and attack them. He could keep it a hundred years, but if he's not meant to use one, it will never work, and it'll eventually just slip away from him somehow. However, if someone is meant to have one, no matter what happens, in the moment where they're ready for it, it'll be there.
Obviously, there are some rare exceptions to this, for example when the Skull Knight gets involved and disrupts things, but those are the general rules.