Thundermaw Hellkite

[Xaol]

Correct. If you flicker it in response to thundermaw, it will be back in play by the time thundermaw resolves, and will still get hit by the damage. It's not being targeted, so flickering it and making it into a new object as a result won't matter like it would with a target-related spell like doom blade.

With the same being true with flickering to get around a  {Terminus} or other board wipe, correct?

[Coffee Vampire]

Yes. Also sacrifice effects like {Tribute to Hunger} and {Liliana of the Veil}'s -2. However spells that target will fizzle if the target leaves the battlefield, including sacrifice spells. Ab example of this is {Mercy Killing}.