That is why all rulers should be heroes, it was surely sad to see my oldest charry die but that is the risk of heroes. And the death of a ruler on the battlefield is truly awesome.
I agree, a ruler hero makes everything more interesting. And it helps to keep interest alive. Who wants to be part of a realm that has a permanent ruler? Unless the player decides to retire his char, he can sit in his capital and rule away (mainly in monarchies, tyrannies and theocracies).