Okay, some updates -- this was a little disturbing, but hats off to the dealer for how they are handling it.
I got the bike back, new cylinder head assembly, $0. I rode 30 miles up into the mountains at 25-50mph with no issues. The next day, I went to a doctor's appointment. I topped off my gas, and then headed home a different way that involves a faster road.
After ~5 miles at 50-60 in 5th, the bike straight died. Battery light, total power loss, and suddenly I am just coasting in traffic. I'd been riding like I wasn't sure the bike was sound, which probably kept this from being very scary or potentially worse.
The bike would NOT fire back up. After a few minute wait, it did, but would not idle at ALL, died instantly when not throttled -- so I gimped it as close to town as I could before it just totally died, then stashed it in the driveway of a friendly but extremely suspicious woman, and actually hitchhiked back to town, my first time trying to thumb it in ~20 years.
I had a bunch of back and forth with the dealer. Basically, at this point, they are going to have to do MORE invasive stuff to the bike, and I don't want a bike that's been this chopped up at 800 miles. Also, after that last fail, I just can't imagine ever really feeling "safe" on this unit, I feel like there's some deeper problems with it.
The dealer was very understanding of my point of view. If I was trying to get full cash back, it might be a slight battle, but it sounded like they were willing to cash me out at pretty close to that. But, really what I want, is a bike that works, and not to be towing it back and forth all the time. After talking to corporate, the dealership offered to give me a brand new (different) 2019 Himalayan for $0, and also to drive and meet me half way so that it's less of a chore for me.
I think that's a very reasonable offer, so that's what I am doing. For the moment I believe the dealer when he says he's sold a bunch of these, and aside from people dropping them at speed, mine is the first one that's had any weird bullshit around it. So, if I really just got unlucky, then bike #2 should be solid and off I go.
Fingers crossed....