I'm not sure, but someone in this thread (
http://www.shrapnelcommunity.com/thr...fpart=all&vc=1) seems to think that Never Healing Wound disappears more quickly with Gift of Health. I'm not sure, but I do know that both Immortal Wraith Lords and afflicted units with the Chalice have still had Never Healing Wound 10 turns after getting it. I believe it can be healed, but expect it to take a long time. I haven't noticed that Crippled takes long for an Immortal to heal from.
Wish I could give you specific numbers; perhaps if you run the game with a high level of debug (-dddddddd from the command line) it will tell you more.
-Max