I didn't necessarily code anything that would make that happen, however, check at game start if Alfred is Aethelred's heir? That's the trigger that would lead to his death in 365 to 730 days.

Alfred is the heir in all of these games. I've played each of the games for at least 730 days and he does not die for some reason I don't understand what is causing it.

The event is bookmark.0001
The trigger is
trigger = {
this = character:33358 #Æthelred
is_ai = yes
exists = player_heir
player_heir = character:7627 #Alfred the Great
What this means is that the event will happen if the character is Aethelred, he is AI and Alfed is his player heir then it should occur unless you are using another mod which changes the bookmark.0001 event.

I'm just using the mpe json with no added mods. I tried to verify my game files but that did not work either. The games definitely meets the requirements for him dying. I'm going to try reuploading the json to see if that works when I get home