I once saw a Caravan get turned over like that... on the A5 heading from Oswestry to shrewsbury... on the uphill stretch away from the esso garage services roundabout at the oswestry end ...
I saw it start to oscillate, and made the executive decision to floor it and get well past it before it flipped over and landed on my bonnet
(back in the early 90's in a VERY fast Sennie B)
I passed him in about 2 seconds flat, and then watched the horror unfold in my rear view mirror..... as soon as I was sure it was going over I phoned the emergency services, it went over as the 999 operator asked which service I required.... since it took the Volvo 360 towing it with it, I suggested all 3 might be an idea...
slightly naughtily, and to my shame, (, yes really, it's still a slight twinge on my conscience 15 years later) I didn't hang around to do more... I was on my Way down to High Wycombe and had to pick my 4 year old daughter up from School at 3, while my wife & her family were at her father's deathbed in the hospital... it was already 12.45 , (now THAT was one seriously unplanned journey! at ANY other time I would have stopped and gone back to help. It was a tough decision... and I was torn... I explained my dilemma to the operator, and carried on... giving my name and both addresses (splitting time between a house on Anglesey, and the house in Wycombe at the time because of work) in case they wanted a later statement and to satisfy their records... I never heard anything on it though.
I still wonder, and hope, that everyone got out okay in the end....