Well, theres a lot of things like that in the manga, like nobody seems to remember when crocodile skewered luffy with his hook, then left him under thousands of pounds of sand, while a mummy, seems like that would be lethal, and even so, that hit seemed to have severed jimbei's spine, as well as burning his lungs and who knows what else, yet he doesn't even have a single mark on him.
That aside, in OP there seems to be something to be said for willpower, not even including haki, irl it is possible to survive wounds and diseases by willpower alone, just by willing yourself conscious, it is possible to avoid drowning for a longer time, I've even heard stories of people surviving shots to the head and other serious wounds, as well as stories of parents surviving fatal illnesses just long enough to see their children graduate and then dying shortly thereafter.
In OP, serious, and even fatal wounds can be overcome with sheer willpower to a much greater degree, we saw that well in whitebeard during the war, since he had just a human body, but yet he kept fighting regardless of damage until the point when his hope ran out, and only died when he had no reason left to keep fighting in much the same manner, though clearly some things, like, say decapitation would be bound to work anyways, this is a real life, documented phenomena, whereby if one organ fails, another organ, or nerves or anything else can compensate, to prolong life for a very long time, OP just takes it much farther, allowing Rob Lucci to survive his wounds, albeit barely, and in fact many people who suffered lethal damage to go on to live a long, full life just because they had the will to live.