Before 1.66 path I used "allowDamage false" in a script to prevent unconscious players waiting for revival to be killed by enemy players.
After the 1.66 patch the "allowDamage false" command doesn't seem to have any effect on the player (tested with 2 players, command was executed on all client computers for the unconscious player that could still get killed).
Same result with any other script command/event handler I could think of (HandleDamage, MPHit).
So the only solution to this is for BIS to add a new Revive parameter that disables killing unconscious players.
Or second option, integrate this invulnerability of unconscious players in the "Basic" mode (ReviveUnconsciousStateMode = 0;).
If you think about it from PvP gameplay perspective : what's the point of adding revive system if players can systematically remove the possibility for revival by just shooting plenty of bullets at an unconscious player just to make sure he is "unrevivable".
It completely kills the point of having a revive system at all. It's not realistic but it improves the gameplay for some players.