When a playable character dies, they get saving throws, followed by the ability to resurrect them.

When an allied NPC like
Isobel or Hope
gets their hp down to zero, they die instantly.

1. that hardly seems fair.

2. It can happen way too easily. for me both of these died in the very first turn of combat, to strong attacks from just one main enemy.

3. It had huge consequences for the entire campaign, changing the course of events.

The result of these, is that I felt a strong need to reload and try again, thus making me feel like I'm cheating - but the alternative was too much.

I suggest when all npcs are downed, they should get death saves, with the chance to be helped, followed by a few turns in which they can be revived. I realize protecting them is a part of the challenge in these fights but it's hard enough with death saves, if enemies do try to execute downed entities.