State based actions do not use the stack, they happen BEFORE any triggers even make it to the stack. So order of triggers is irrelevant, since there are no triggers to order, the game is already over. And for objects still on the stack, they don't get to resolve, because the game is over.

If you mean, that you should have been able to put your Syr Vondam triggers on the stack above Sephiroth's drain triggers, you are wrong. YOU were the active player, so YOUR triggers (all of them) have to be put on the stack first. THEN all your opponent's triggers go on top of them and resolve first. You lost, because it was your turn. If the creatures had died during your opponent's turn, then YOUR triggers would have been on top and resolved first.

but these abilities must be added to the stack at the same time (after the creature has died), and if they had worked in a different order, the match would not have ended.

You seem to seriously misunderstand some fundamental rules of the game. You lose for having 0 or less life as a state based action. You lose for having 10+ poison counters as a state based action. You lose for having tried to draw a card from an empty library as a state based action (though only the very next check; if you survive through that check somehow, the game will no longer care about that particular instance). State based actions are checked every time right after any object on the stack has finished resolving (and in the cleanup step), and all state based actions requiring the game to act are resolved as a simultaneous event. State based actions DO NOT WAIT for the stack to be empty. You lose with the very next check, end of game.

The thing that requires the stack to be empty is the game's progression to the next step or phase. Which also requires all players to have passed priority in succession while the stack remained empty.