When I said he wouldn't have a problem selling it, I was meaning selling it pre-flood condition, as the other person mentioned he may have issues liquidating it quickly had the need arose, hence the possibility of insurance fraud. I just stated that a P1 in top condition (his pics he took in IG before Ian) he could sell it in a day.
To answer your question? Yes, it could come back good as new if it were sent back to McLaren in Woking. They would completely disassemble the car down to the Monocage 1 carbon fiber tub. See what could be reused, and fit new things. Cost would be up there, but probably not what the car is actually worth retail.
Plus, McLaren is known to keep their super limited cars on the road. Look at what they did to Mr Bean's F1. Fixed it twice, once with the engine actually getting thrown out of the car. He resold it no problem for like £15M. The thing that some forgot with this car, is it's a hybrid with a full electric drive system. Yeah, it's only for a few miles, but still has hybrid batteries. That could be a positive if rebuilt as they would use the latest battery tech vs when the car came out the end of 2013.
I really don't see one of the YouTubers getting this to rebuild. I remember how hard of a time Tavarish had rebuilding his 675LT. Parts were basically unobtainium. Figure this x10. But someone will buy it once it hits Copart (unless the owner buys it back). Just watch for AZ Cycle Parts on IG/YouTube. They buy all the wrecked exotics, strip them down and sell whatever they can.