When the Heirloom Ring break, can you get it back by choosing this Specialty again during Getting Better? And Does Miraculous Escape suffer from Malice?
In general, you can only take a given Specialty once. Once you've broken the Heirloom Ring, you can't get another.
For stuff like Miraculous Escape where you do Break but you automatically pass the Stability test, you can still suffer Malices. On the other hand, Languished's Rock Bottom lets you ignore all consequences from Breaking, and this includes Malices.
These are mostly up to the GM. I'd personally say yes to changing NPC Morales and recruiting monsters under certain circumstances, but different GMs may handle this differently.
With NPCs, their stats are meant to be written in a simple and quick way. You could give them a full PC style set of Abilities, but this would take more work and slow the GM down when they introduce a new NPC. The recommended thing to do is give them specific skills (e.x. Climbs Walls DR 8) when relevant, and then you can modify these further with circumstantial bonuses and penalties when appropriate. But if an NPC is really important, you could give them Abilities instead.
For Dusty Sachet Of Bitter Herbs: If you choose not to make the tea, will you die? Or is this Werewolf curse different from the normal one? Can Dismiss into Figment affect gods? Like can I Dismiss into Figment the history of King in Yellow?And Is the DR 16 on Leash The Departing Soul for the Haint to turn or not turn on you?
For the Dusty Sachet, this is open to GM interpretation. I think I'd rule that it has a slower progression than normal pollen lycanthropy, that way the player doesn't finish turning into flowers between investigation 2 and investigation 3. But the disease will finish its course unless cured---whether by drinking the sachet's tea or by some other means.
Dismiss Into Figment is a little weird, since it affects Toughness. You ignore the Toughness part when it's used on NPCs and monsters, since they don't have Toughness, but otherwise it functions the same way. That said, it only affects a piece of a target. You would need to rapidly and successfully cast a lot of it in succession to whittle away at a god. With enough casters and hit points and a chained down god, you could do meaningful harm to it, but you would need a significant population dedicated to the task.
The Briefly Turn On You DR 16 that Haints created with Leash The Departing Soul have is the difficulty for them to attempt to hurt you. So on a 17+ they can throw an object at you or try to terrify you. The GM rolls this whenever they judge appropriate.
Dismiss Into Figment is better at handling small, mortal targets than big complex things. Thus it's not quite a silver bullet for gods (nor can you do something like target the earth and dismiss humanity from its history.)
King In Yellow is also a tricky target for this spell, because he's already got a very loose relationship with reality.
I'd say that you can use Dismiss Into Figment on people or places to erode their relationship with him, and that you could use it on him to temporarily redact small parts of his lore, but also that he can recover from the effects of Dismiss Into Figment over time as his nature repairs the gaps in the fiction.
If multiple casters simultaneously hit him with Dismiss Into Figment while in Carcosa, that would take a serious chunk out of him. Similarly, if a large number of casters repeatedly spammed Dismiss Into Figment on Carcosa itself, they could try to break the association between Carcosa and the King and potentially free the city (even if this wouldn't guarantee the King couldn't just re-take it.)