Everyone caught a break when the regular spillway was able to handle the increased flow without rapidly eroding back to the base of the damn. It looks like the hillside that both provides the regular spillway exit route abd anchors the north side of the dam is made of pretty solid bedrock.
That's the key to this entire emergency: is the bedrock solid enough to allow them to continue @ 110k? For how long? It's really a race against time, but so far the regular spillway appears to be handling the situation. (Which of course could turn on a dime.)
As for future repairs/rebuilds, I wonder if they will simply build a monster catch basis lined with 15' concrete where the current cascade is falling at the end of the remaining regular spillway? That's a mighty deep cavern now that would take endless amounts of substrate to re-fill. It's probably why the problem occurred there in the first place. Might make sense to use the natural bedrock formation/elevation drop as the basis for the new spillway.
It perhaps would depend on the quality of the bedrock from the break out to the outflow channel. Regardless, I betcha the new fix won't scrimp on rebar and quality/quantity of concrete.