Should Destiny allow you to respawn immediately, without waiting around, without the countdown?
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They have said that revivals will give the same amount of points as kills, so reviving will probably be a major part of PvP as well as PvE. My guess, which is just a guess, is that there will be a respawn delay, during which your allies will be able to revive you. If you get revived, you get to keep your heavy/special ammo and your rescuer gets points towards his super. Again, that's just a guess.