BA/VS connecting flight question

[I posted this in the middle of another thread, but I realise it was somewhat off-topic, so I'm putting it here if that's ok.]

Let's assume you have a single connecting 'business class' ticket (for example AMS to JFK via LHR) in which the first AMS-LHR leg is with BA CW and the second LHR-JFK leg is with VS UC.

If BA mess up (a delay, for example) and you miss the onward VS flight, what happens? I presume it's BA's obligation to get you to your destination, but what is likely to happen in reality?

I assume you just get put on the next VS flight in UC, without too much bother (I would hope)? But if that flight is full, would you get put on a BA flight in CW? What about miles/points etc?

Does is matter, in such a case, from whom you purchased the fare? For example would it matter if the fare is purchases from Expedia, rather than Virgin?

If it's on one PNR you should be covered, but I would expect that you would slimiest certainly be put on a BA flight. Nog sure about the tier points/miles. If it's two separate PNRS then you would probably not be protected. I don't believe it matter who sold you the ticket as it's the fare rules that count.

I did this last year I was at AMS on the plane just pushed back when the flaps would not extend so the flight was canceled.
Thankfully I had left myself enough time to get on the next BA and still make the VS45.
On re-entering AMS BA attempted to put me on a direct flight operated by DL.
I refused saying I could still make the VS45 and so they gave me a seat on the next LHR flight which was on time and although I had less time than planned in the clubhouse I still made my first upper class flight.

So yes if BA mess up they will re book you of you are on one PNR