Each group/situation has their own rules. Whilst at practice (so it's just 'out', rather than 'dead') we take two hits (or more for newbies/if you're wearing armour).
Alternatively, I've been in a battle where it was "If you're hit once, stumble back and don't move. If you're hit again whilst you're like this, you're dead". It was fun - kept people in the battle a lot longer.
Now for my particular group, in terms of 'degree of death', when we're doing local shows we have 'wounded'. Like, the crowd knows we're not "dead" so it then becomes much more believable if we just sort of .. limp and act as though the force of the blow has done its damage.
Get a lot of "ooo" and "ahhh"'s buy that style - my personal favourite.
To signify the end of the event/resurrect the fallen, I've heard a lot of groups use the phrase "Dead Arise".
But again, every group/situation seems to have its own rules.