Waverider's words suggest that Doomsday's body could have been completely destroyed after his battle with the Radiant, suggesting that his healing factor has its limits, but at this point Doomsday was left so damaged that he remained 'comatose' for several thousand years while trapped and cut off from the solar energy he required to sustain himself, making it unlikely that anything is capable of doing sufficient damage to him to bring him to this state again after his subsequent evolutions.