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The best way to answer the first question is addressing the responsibility to make the dam & spillway structures as safe as reasonably possible. This is known as "As Low As Reasonably Practical" or ALARP. This is how Risk Management of systems is measured by.

The degree of ALARP is proportional to the risk to life & property. Oroville is in the highest risk hazard category in this regard. Thus, it is required to have the highest degree of ALARP in KNOWN conditions of the Dam & Spillway.

As it was well illustrated in the recent "NBC Investigates" TV news show airing, the retired DWR engineers and other reviewing engineers revealed inside information that DWR is not operating the Dam & Spillway to these required stringent safety conditions.

So, by these modern standards, which are also applied to nuclear power plants, nuclear powered submarines, FAA aircraft maintenance, etc - DWR has failed. DWR cannot assure the public that the risk is as low as reasonably practical. In essence, with the UNKNOWNS, just like they found out in the two spillway failures, there are uncertainties that remain that are not 100% tested and KNOWN - such as the internal phreatic water condition inside the dam.

The DWR insiders also testified in interviews about the 16+ foot crack in the headworks, and about the cracking & failing anchor tendons in the headworks. DWR admitted that the loss of control of a gate or gates means the risk of loss of control of flows (potential failure mode). Evidence tends to support that there is a real failure mode in a "jamming" risk from a problem in Gate 8 (and possibly Gate 7 as a trunnion pin anchorage is shared).

Just like NBC noted, DWR kicked the can down the road on important issues that were known years ago. Now they face not having the time to respond to prevent a failure (it could take a year or longer to fully replace the headworks).

If DWR miscalculated their choice of using seepage at the toe drain as an indicator to replace a KNOWN method of determining the dangerous internal swelling from a pressurized phreatic condition in the Zone 3 embankment (using piezometers), AND the highly fractured left abutment is drawing water away from the toe drain system (including "clogging" effects), then the dam risks exactly what NBC showed in their graphic - a sudden onset in days of a catastrophic collapse of the dam (just like Teton in 1976).

As for the second question: If the headworks or the dam fails, it doesn't matter what has been fixed on the new spillway. Keep in mind that they placed ~3,000 rock anchor bolts in the 730 ft of the leftover original Upper Spillway. This is an extreme level of anchorage to slabs that DWR purported was "safe" and is "doing fine" before the BOC told them it wasn't (actions speak louder than any non-spoken item or redacted item in BOC memos).

The only item on the new spillway that is structurally "off" (i.e. mismatch) is the high ratio of anchor bolts & plates in the sidewall slabs compared to the structural intersection strength of the vertical sidewall (weaker). If you calculate the combined strength they believed necessary for this higher density ratio of anchor bolts & plates in the sidewall slab, it doesn't match the structural design capacity of the intersecting rebar at the base of the vertical sidewall.

However, the new spillway is so much better in design and structural improvements over the original that this spillway fully meets modern standards with a good Factor of Safety well above and beyond.

the dam risks exactly what NBC showed in their graphic - a sudden onset in days of a catastrophic collapse of the dam (just like Teton in 1976)

That sounds an awful like we're at the brink of final stage failure needing only a final shove of enough water. I suppose technically, we're not into the final stage until the actual physical failure has begun - ie. the "domino affect" has begun that can't be stopped.

If I were living in Oroville and were following your and the NBC analysis here, I would have figured out a way to move even knowing that selling my house might be impossible - I'd be potentially saving our lives.

I'd move and rent or something until either the dam broke and hopefully insurance would cover the house or somehow this thing were fixed over the next year(s) in time to move back. I think I'd have ground for a suit to cover the expenses.

I would think a lot of people would be doing this right now.