Answer:
you can die from:
old age
hunger
drowning (put a fence around the pool)
fire(not with the brave trait as they will extinguish the fire)
electrocution(repair object in a puddle, wont work with handy trait)
thirst(vampires in late night)
mummy's curse(fight a mummy in world adventures)
meteor(ambitions)
your sims will turn into a gravestone and their ghost will somtimes come out between 00:00 and 06:00, and with a special chance from the science lab you can make them playable.