Just a config option on dedicated servers to let the timer keep going even if the player is logged out. To implement this, perhaps you could store the system time of death as nbt instead of how much time the player has left, and then compare this to the current time + config to determine the countdown timer. Will understand if this is too difficult, but it would be really nice if possible.

• reason -
  I run this on my SMP server (non-hardcore), and want to have the revival mechanic as a nice bonus for being near other people, as opposed to players logging out when they get K.O'ed and waiting for someone to come rescue them.