Ok these are some extreme situations.
I have seen price manipulations for profit on defi, but those are usualy a flash loans attacks that happen in one block. In the case of Hive and the 3.5 days feed price it is not possible for flash loans attacks. It will be needed some serious capital to do this manipulation, but this been crypto cant exclude anything, even the 50% drop from regular market moves.
The end game will be to much debt, debt limit reached and hbd worth less, meanining it cant last long. Also not sure will any fee save us from this scenario :)