Friend of mine has actually said..."plane hijacked, landed and hidden so PAX organs can be harvested and sold on the black market." Seems reasonable.
The key point is that the hostages have an intrinsic value as hostages. If one of my loved ones were on this flight today's news would have given me optimism. I don't think that the sale of organs makes much sense. Easier to kidnap low-value 'invisible' folk from the bottom tier of society, not somewhere near the top.
It could be that having landed intact (albeit perhaps not in an airworthy condition) the hostages may be on their way to some safe secluded place where their life needs are met with no means of escape or communication. Meanwhile, the hijackers make their way to some other place and make whatever demands they wish. They will promise to give the location of the hostages when their demands are met.
Provided the demands are of a political nature, they could get away with it.