My question is, if a powerful demon spirit wants to hurt you or destroy your life because you have offended them, would a divine hindu God like Krishna be able to save you and keep the entity from causing you harm?
It could work! But the nature of this is the spirit is hexing/crossing you! Just like a bad luck mark on your back! You can wait for someone to save you or you can save your self! This could easily be solved by performing an uncrossing ritual! Banishing bad energies! Calling the spirit that’s mad at you and offering it peace if you offended it! Most spirit ain’t there to get you unless you offended them! So offering them something and making peace with them gets them on your side and most even will go out of their way to help you!
That is a really tricky question that doesn’t have a single answer
Yes, because “demon” is a concept from division of the world and your soul (hint - same thing) into “God/Good” and “Evil” and Sri Krishna is a gateway to a reality beyond that kind of concept, he fucked them ladies and he killed them enemies (Bhagavad Gita) and he was still pure.
Sri Krishna is YOU, what you need to do is read Bhagavad Gita until it hits you like a brick and you can laugh in the face of immiment genocides, etc.
But - BUT - then also go out and do things about them.