It's assumed the grandma took his place(she can change form), which makes sense considering she doesn't exist in the current manga, with her devil fruit transferred to Bon Clay, all suggesting she indeed died. However, the viz translation makes it seem like it's really Orochi since he knows exactly how crazy Oden can be.
So unless the grandma somehow intervenes to take the hit for him, it's indeed curious how he survives. Only Kaido can potentially save him at this point lol