"... cut off the damaged riser..."

???!!!

That has been an option since day one? That was my first thought... if you can cut it off square, you can use a compression collar(sss) and threaded rods or even cables to blind plate it and then encase it.

I simply assumed it wasn't an option due to the possibility of ignition of the plume. Why else would it not be underway?

Oh... ahhh... maybe it's become a scapegoat option due to the consideration of burning the plume that washed (and is washing) ashore?

Better minds are at work than mine so I'll just hope they do a good job and get lucky too.