Just my two cents, but there should be a harsh skill lock to prevent earning experience or new skills. Maybe a timer that only counts down when actively logged in, or an xp debt that has to be worked off.
Games without a harsh penalty for dying do not reflect realiism in games. For example, in a real battle, nobody would just charge in. There would be tactics invovled and players would think through their actions. When games have no penalty you get players who attack without thinking, making it harder in the long run for players to take or keep positions because of the loss of numbers.
Another penalty could be something as simple as longer and longer respawn times upon death, which reduces as you remain alive.