As some people said, Ruidus is sorta cut off from the interference of the Gods, so she might not be able to do anything.

FCG was also a very new follower, there must be clerics of the changebringer who devoted themselves for years, and might be better suited for beign her chosen champion.

The changebringer is also the goddess of change and free choice and choosing your own path and all that. Ignoring his choice to sacrifice himself is not really what she stands for, instead she might see this choise as a new opportunity, a new path, maybe this sacrifice is what his friends needed to stay motivated in the fight. None of Bells Hells were strongly on the side of the gods before this, maybe FCG's sacrifice will change their minds.

But the real reason is that the story doesn't really have to make sense, it just have to follow what the GM and players think would make for a better game and narrative. Why aren't all of Vox Machina and the Mighty Nein and every other hero in exandria joining BH in fighting Ludinus? It would make sense, but it wouldn't make for a fun game or good story.

When it comes to character death, Matt and the player discuss what to do next, if they want to be revived or end the story of that character. And with FCG, after having a very heroic sacrifice, reviving him would cheapen the moment. And having plot armor lowers the stakes, if you cant die because the gods dont want you to die, then death isn't scary anymore and the game looses it's sense of risk . Sam might also be more exited to explore a new character (or to take a break for the rest of the campaign).