This would also be my diagnosis. Had a Peugeot 504 Diesel that got to
223,401.2 miles in the hands of my then college attending daughter. Same
situation. It took off on a freeway onramp outside Arcata and wouldn't stop.
By 90 mph she realized that stopping was essential. She pulled the car off
the road (eventually) and she and her friends ran for cover. The pitch
continued to go up (she was a Liberal Arts major so there is no quantitative
data available) then black smoke. This was followed by the sound of a loud
dentist's drill and white smoke, then a series of loud retorts. (She was
describing this in certain musical terms I couldn't relate to!) Finally some
dull metallic sounds and (she reported) the jumped up and down. Then much
sizzling and ultimately calm and quiet. At this point she noticed several
shocked spectators including a CHP officer and observed several large bumps
in the hood surface. When she opened the hood she said that there were bright
shiny pieces of metal everywhere. Also said that the big long thing in the
middle of the hood area had a huge hole in it. Needless to say she used this
event and some blither about post diesel traumatic stress syndrome to
leverage her way into a Mazda.

I have always thought that the first stage involved the consumption of oil
blow-by, then the oil and ultimately the Aluminum of cylinder head or piston.
Consider yourself fortunate as others have noted!

Frank Grunthaner