Even with it, izangai seems to have limits. For example, when Madara was able to revive himself it did not heal his wound recieved before death. My guess is that since Obito's essential life force was already drained from having the tailed beasts and gedo meza extracted from him he would only be able to rewrite the death that kaguya just did to him, and he would still die later from his life force being drained from the tailed beast extraction. So it wouldn't have mattered if he did ressurect himself.. It could also be that there wasn't enough chakra prepared for izanagi, he wasn't in the right mind set, the disintegrating bone stops it, he thought he would be able to give kakashi both eyes if he used it, If he used it he thought he wouldn't have been useful anyways, he thought he deserved to die, he wanted to die. I mean there are honestly a myriad of options and combination of options. Take your pick.
