if a demon took your soul then yes, you would go to hell, as I assure you no demon takes souls to walk them to the pearly gates of heaven. However, if you are possessed by a demon, it means that your soul was at risk of eternal damnation already. Hence, unless you find god and you get exorcised, you will not see the beauty of heaven.
I'll just assume there are heaven, hell, souls and demons for a moment and answer your question: If a demon ate your soul, it'd mean your soul would vanish, right? So no, you wouldn't go to hell, your soul would just stop existing.Or if they took your soul, then it means that your soul is theirs now, so you wouldn't have anything to do with heaven and hell.
We may give our soul over to all manner of demonic influence, but we decide to do it. The commission of significant sin requires an exercise of the will. Can we unwittingly err? Perhaps, but the worst kinds of sin are when we choose to do them.
That cant happen unless you willingly allow the 'demon' to use you that way. The fallen angels that are what we mean when we say 'demon' (as opposed to the Hollywood versions) do not have the power to circumvent the free will God gave us. A so called 'demon' can only have control of your soul if you allow it. And then, yes, if you willingly choose satan by allowing one of its angels to have control of you, you will go to hell.
No. Not until I have overdosed myself with enough cool-aid and opium consumption to have lost all my brain controls and senses to differentiate my superstitious fantasies from reality; and certainly not unless that demon (one with a digestive system, of course) ATE my soul with dry martini!!