This is certainly an issue going into the future. Dams, and especially dam components like spillways, are not design to last forever. 50 years is pretty good, 100 tops. Certainly not multiple hundreds, though earthfill structures like Oroville might last hundreds if well maintained.
Doesn't seem like a maintenance problem though (on emergency) from all these links, but a lack of sufficient spillway construction/design robustness and armouring. Some probably don't need it, but look at (google earth) the slope downstream of the emergency spillway, it's about 10H:1V, a very steep hill.
The big concern as I see it is that they are now worried about
any water being up against the concrete face of the emergency spillway, hence the call to lower the pond elevation by 50' (the emergency dam is 59' tall by my google estimate). There has been severe erosion downstream, which has saturated the ground that has never been saturated like that before, and a significant weight of soil has been removed from the downstream toe of the concrete structure as well. The major risk now is the footing of the emergency spillway might slide, causing the concrete to fracture and the emergency spillway to literally "split open".
The good news is it looks like there is significant fill (beach) on the upstream side of the emergency spillway, it is only 25' high on this side, and they said yesterday that the water is already brought down 20 feet from max. So likely there is no water against the concrete of the spillway at this point.
It will be interesting if they slow the rates of the main spillway now, once the emergency spillway is not in a critical state, to stave off the "head cutting" up the main spillway.
The main spillway eroding is the primary concern here, both from a protecting the Oroville dam, and a "how the hell did this happen" perspective. It is not surprising the emergency spillway had severe downstream erosion when used. It IS surprising that the main spillway failed due to full bore flow through it. That may have been a maintenance issue, and really shouldn't have happened.
With its location next the dam, if the main spillway is lost the dam could very well go too, if the emergency spillway breaks, it may not make its way to the Oroville dam and take it out. You'd be looking at only partial drainage of the reservoir instead of full, and at flow rates a small fraction of a Main spillway/dam failure. Of course it may progressively take out the main spillway and then dam, but the chances of that are lower than a direct main spillway failure. Likely (hopefully) there is enough distance and elevation built into the main spillway so if it fails and flows uncontrolled it will not affect the O Dam. From google earth again, it appears there is some significant material between the two, though whether it is constructed fill or bedrock I'm not sure, but it is slightly reassuring.
Anyways - back to my breakfast mimosas on the beach (Cancun)
But I couldn't resist following this story even on vacation.