There is a very short, one paragraph-long Wikipedia article on nitya-samsarins, or eternally transmigrating souls, as classified by Sri Madhvacharya. Sri Madhva also classifies souls into mukti-yogyas (those eligible for liberation) and tamo-yogyas (those eternally condemned to dark hell).
At first glance, this seems like a stark contrast to the contemporary Shaivite view (such as that described in the book Dancing With Siva by Satguru Sivaya Subramuniyaswami). In this view, all souls are eventually destined to achieve moksha.
So which is it? Is a state of eternal hell possible according to Sanatana Dharma, and if so, under what conditions? Is it something to be feared as much as, for example, some evangelical Christian sects emphasize a strong fear of hell? Can the Gods, devas, tapas, or the accrual and transfer of merit, help uplift a Jiva out of Naraka? And are such events eventually destined to occur under Shaivite doctrine, since every Jiva eventually gains liberation? And if this view (the Shaivite one) is true, then how does universal liberation happen (e.g. could it be that someone is trapped in hell for aeons until dissolution, or pralaya, trivially "liberates" them?) Are the Vaishnavite Madhvacharya and the Shaivite cosmologies compatible?