In the Legends novel Shadows of the EmpireShadows of the Empire, Darth Vader does use force healingForce Healing. In the movie Empire Strikes BackEmpire Strikes Back, the time you see him with his helmet off-is actually a chamber he uses not only for communication, but also to focus his time into healing the permanent damage. In the SoE book, he uses as much hate as he can, but can only remain outside his breathing apparatus for something like 15 minutes, and it causes him pain to even do the act-using more rage to make himself last longer each time.
It may just be legendsLegends, but it fits into the cannoncanon universe.