Is there a high death rate from pericarditis ?being treated with naproxen.

Depends on cause: Often caused by virus usually self limiting but may need colchicine added to prevent recurrence. More serious if caused by bacteria ir fungus or things like TB,HIV,etc. if it persists may eventually need biopsy if cause unclear. Should be followed with echo. In rare cases may require surgical removal to prevent trapping heart but fatalities rare with treatment