I think it's a plot hole. If you think that the Mangekyo was awakened for a moment, since we saw when he really awakened the Mangekyo, it may be a healing technique that he used to save just Obito's right eye, not his entire body. But I can't imagine his Sharingan being the savior because in that case Obito could have managed to slip through the rock with his entire right part of his body.