They only go away when an effect instructs a player to remove rad counters from themselves
Krenkos Buzzcrusher was apparently worded like this to enable it to remove Lotus Field in Pioneer
Tap three untapped Zombies you control: You draw a card and you lose 1 life
Its extremely versatilesometimes it protects your creatures, sometimes it removes blockers, and probably most often, it answers any number of stax-type creatures that are interfering with your plans long enough for you to win
According to PokRev, it can get pretty serious
Sephiroth, the Savior Four colors and 7 mana, but basically you win the game. Ideally youll get Atraxa, Grand Unifier earlier so you can build around it, as its among the best payoffs for UGx Towns