There are no one hit kills in the game at all, there aren't even one hit incapacitations. When you lose all of your HP, you are downed, and in order to actually kill a person, you have to shoot them so more or go in and melee them. because of the whole downed thing, there's really not any point where a killcam would make sense, looking around for a medic is more useful, and its not very important to know how you were killed while downed.
Yep, otherwise medics don't have to chance to revive people. That's also why you respawn in waves. Having your whole team death can be a catastrophe, but it can also help you to push (Everyone is at full health, full ammo, max ability pips)
Killcams could last for minutes if you die and don't join the respawn wave and no one revives you.