Mortality from GCSE approximates 20 - 25%.
However, it is not clear that prolonged FMSE results in substantive brain injury. Reasonable attempts at control are advocated, but high-risk therapies, such as induced pharmacologic coma are rarely warranted.
Source
Mirski, M. MD PhD and Varelas, P. MD PhD. "Seizures and Status Epilepticus in the Critically Ill." Crit Care Clin. 2008. 115-147.