When you get that low you're already dead, whether you raise it back up to 5 or not. One ki blast, hitting a wall relatively close to you, can kill you. The idea behind the PL dropping is that you're encouraged to go all out before you die rather than hide somewhere and hope you don't get killed. Since you can just respawn after you die it doesn't seem all too important. It would be a feature that would rarely ever be triggered, and when it was, it still wouldn't stop you from losing a big chunk of PL.