Ad Infinitum

"Et sic sedebis, perpetuo vivifica exitio tuo. Semper, spectans maximum errorem, quem unquam fecisti. Hanc unam scenam spectabis, in aeternum. Oblivisci homines qui sis. Corpus tuum strages vile fiet. Et numquam desistet. Perget ad infinitum. Defectum tuum in hoc te coegit. Nunc ultimum defectum vives, et nunquam semper ab aeterno cruciatu eris." 

You fire off a blast of blue light, trapping your foe in their last moments. Their body shuts down, essentially dying. Their consciousness is still active, going through their fatal mistake. Their body will decay, but they will still be alive in their eternal prison.