Apologies, you should use
http://www.ageod.net/agewiki/RulSuddenDeath setting value = 0
The other reference will adjust the morale, but not switch off sudden death.
Use a text editor [NotePad] on the "main" event file for the campaign or scenario you are playing
Look in
\EAW\Events for the file.
Example, for the Great War campaign, open
3 - The Great War.sctPaste this at the end of the file, save and close:
SelectFaction = CMN
SelectRegion = $Berlin
StartEvent = evt_nam_SuddenDeathOff|1|0|NULL|NULL|$Berlin|NULL
Conditions
Actions
RulSuddenDeath = 0
EndEvent
It even will work with a saved game, I think...