Are characters who appear in multiple separate questlines immune to being killed?

[Kotemon]

Not to dig up graves but, does given the people who remember 1.0 and those who finished coil. Where does Louisox fit in the death immunity category of plot armor? Or did he die off for the sake of plot? Then there's Gaius. His ending is kind of ambiguous.

[Fenral]

snip

Quest-givers/main NPCs can die/disappear if all the quests they appear in follow a set linear order, or other circumstances render their quests unplayable (such as the 1.0 -> 2.0 jump). Louisoix was 1.0's Urianger, but since his death caused the version up, the other quests he handed out are no longer available. Likewise, Gaius only appears in Main Scenario quests across 1.0 and 2.0, and since those follow a linear order, there are no complications that can arise from his death (or not death).

It would be quite difficult to justify a change to an active quest if an NPC involved in them suddenly dies or is otherwise taken out of commission by another quest, so the assumption for now is that NPCs in multiple questlines are nigh bulletproof. Given that, it follows that if an NPC could be left hanging by the end of any single quest (i.e. Nero), they can't appear elsewhere without that story being resolved.

Truth of the matter is, the game is simply too new for us to know one way or the other.