From my limited experience with cutting down trees, when oak snag like this, they shed water and don't rot nearly as fast as on the ground. The roots gave way on this one and couldn't support the weight, which leads me to believe it's pretty solid, but you really don't know what's inside till you crack it open.It looks pretty rotten in your pic. I’m have no experience with that species. It looks like once you get the little one out of the way, releasing it from the root wad wouldn’t be life threatening but then it has your signature on it and it would need to be finished.